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Can't binding in ToolTip

I'm working with ToolTip in WPF C#. I want to bind an element property to ToolTip content, but the output is empty. Initially, I used the binding below, and it did not work.
Content="{Binding ElementName=txtf1, Path=Text}"
So I found related solutions here, but the result did not change. Can anyone point me where I'm going wrong?
<StackPanel Height="Auto" Margin="15,10,15,0" Width="74">
<Image Source="/Image/AutoCAD.png" Width="50"/>
<TextBlock x:Name="txtf1" Text="Border19072021 Border19072021"/>
<StackPanel.ToolTip>
<ToolTip DataContext="{Binding Path=PlacementTarget.DataContext ,
RelativeSource={RelativeSource Self}}">
<Label Content="{Binding ElementName=txtf1, Path=Text}"/>
</ToolTip>
</StackPanel.ToolTip>
</StackPanel>

[...] initially, I use Content="{Binding ElementName=txtf1, Path=Text}" and it not work.
Yes, that is because each window in WPF has its own visual tree with elements and a ToolTip and other popups are actually displayed in a separate window. ElementName bindings do not work here (RelativeSource too), since these are different XAML namescopes.
The question you cited is the right approach, but you applied it the wrong way. In theory you can use the DataContext property as binding indirection for the ToolTip, but you should not.
<StackPanel DataContext="{Binding Text, ElementName=txtf1}" Height="Auto" Margin="15,10,15,0" Width="74">
<Image Source="/Image/AutoCAD.png" Width="50"/>
<TextBlock x:Name="txtf1" Text="Border19072021 Border19072021"/>
<StackPanel.ToolTip>
<ToolTip DataContext="{Binding Path=PlacementTarget.DataContext, RelativeSource={RelativeSource Self}}">
<Label Content="{Binding}"/>
</ToolTip>
</StackPanel.ToolTip>
</StackPanel>
The above code works, but the DataContext property serves a core purpose in WPF for data binding. Do not abuse this property for this purpose or you break data-binding down the visual tree. Apart from that, the binding on Label and ToolTip is redundant, as you can see below. There is another property called Tag that you can assign any value to.
Gets or sets an arbitrary object value that can be used to store custom information about this element.
<StackPanel Tag="{Binding Text, ElementName=txtf1}" Height="Auto" Margin="15,10,15,0" Width="74">
<Image Source="/Image/AutoCAD.png" Width="50"/>
<TextBlock x:Name="txtf1" Text="Border19072021 Border19072021"/>
<StackPanel.ToolTip>
<ToolTip>
<Label Content="{Binding Path=PlacementTarget.Tag, RelativeSource={RelativeSource AncestorType={x:Type ToolTip}}}"/>
</ToolTip>
</StackPanel.ToolTip>
</StackPanel>
You can use a RelativeSource binding to refer to the ToolTip.Tag directly from the label. If there are multiple bindings like this, you could consider creating custom attached properties for each of them and bind them the same way.

I reference here, How to binding other element in ToolTip
You have not carefully read the topic you are referring to.
ToolTip, ContextMenu, Popup (and some other elements) pop up over the contents of the Window without changing it.
Think for yourself: How can you introduce new elements into a Window without changing the visual tree of this Window?
Answer: this cannot be done in any way.
Therefore, these pop-up elements are implemented as the contents of a new small Window shown above the main Window (the one in which they were called).
And since these are DIFFERENT Windows, they have different visual trees.
Therefore, it is impossible to find elements from the main Window in the tree of the Pop-up Window (Bindings of the ElementName and FindAncestor types).
You can use an element reference (Binding Sourse = {x: Reference ...}), since references are resolved at compile time and without regard to the visual tree.
Example:
<StackPanel Height="Auto" Margin="15,10,15,0" Width="74">
<Image Source="/Image/AutoCAD.png" Width="50"/>
<TextBlock x:Name="txtf1" Text="Border19072021 Border19072021"/>
<StackPanel.ToolTip>
<ToolTip>
<Label Content="{Binding Source={x:Reference txtf1}, Path=Text}"/>
</ToolTip>
</StackPanel.ToolTip>
</StackPanel>
In addition, the Popup's DataContext inherits from the element in which It is created.
In your case, this is from StackPanel.
Therefore, you can simply set the default Bindings to receive data.
Example:
<StackPanel Height="Auto" Margin="15,10,15,0" Width="74">
<Image Source="/Image/AutoCAD.png" Width="50"/>
<TextBlock x:Name="txtf1" Text="{Binding SomeViewModelProperty}"/>
<StackPanel.ToolTip>
<ToolTip>
<Label Content="{Binding SomeViewModelProperty}"/>
</ToolTip>
</StackPanel.ToolTip>
</StackPanel>
The PlacementTarget property is used to change the target element for the popup.
DataContext inherits from this element.
If it is not specified, the DataContext is inherited from the element in which the flyout is specified.
You don't specify it, so it is null, which is what your binding returns.
Example:
<StackPanel DataContext="{Binding Text, ElementName=txtf1}" Height="Auto" Margin="15,10,15,0" Width="74">
<Image Source="/Image/AutoCAD.png" Width="50"/>
<TextBlock x:Name="txtf1" Text="{Binding SomeViewModelProperty}"/>
<StackPanel.ToolTip>
<ToolTip PlacementTarget="{Binding ElementName=txtf1}"
DataContext="{Binding Path=PlacementTarget.DataContext,
RelativeSource={RelativeSource Self}}">
<Label Content="{Binding SomeViewModelProperty}"/>
</ToolTip>
</StackPanel.ToolTip>
</StackPanel>

Bind element inside of datatemplate to parent's property

how can i bind an element inside of a template to a property of its parent like:
<Button Tag="rofl">
<Button.ContentTemplate>
<DataTemplate>
<TextBlock Text="{ HERE I WANT TO BIND TO THE BUTTONS TAG }"/>
</DataTemplate>
</Button.ContentTemplate>
</Button>
Is that possible?

In addition to #Pedro Lamas's answer you can also perform this by the following way:
<Button x:Name="ButtonTemplate" Tag="rofl">
<Button.ContentTemplate>
<DataTemplate>
<TextBlock Text="{Binding Tag, ElementName=ButtonTemplate}"/>
</DataTemplate>
</Button.ContentTemplate>
</Button>
You define a name for your control and access it's property in it's DataTemplate thanks to the ElementName feature.

You should be able to use a RelativeSource with the TemplatedParent to do that:
<TextBlock Text="{Binding Tag, RelativeSource={RelativeSource TemplatedParent}"/>

Value from Binding ElementName producing empty string

I have a Datagrid which has a DataGridTemplateColumn containing a ListView whose Itemsource is bound to an array of string.
Within that ListView I have defined an ItemTemplate as I want the Foreground of each item in the list to be dependant on condition - so that's applied to a TextBlock.
I want a tooltip to display when each item in the ListView is hovered over, so I have a Tooltip defined in that TextBlock
What I'm trying to do is have that Tooltip display the title/detail about a specific item by using a converter (to get the index of the item in a different list).
For this I need the Tooltip to know the ListView item but I can't seem to get that to work. The TextBlock itself retrieves it using Path=., I have tried naming the TextBlock ListItem and retrieving it as ElementName to no avail - the result is just empty string.
Here's the relevant xaml (with formatting properties removed).
<ListView.ItemTemplate>
<DataTemplate>
<TextBlock x:Name="ListItem" Text="{Binding Path=.}" Foreground="{Binding RelativeSource={RelativeSource Self}, Path=Text, Converter={StaticResource ConvertItemToColour}}">
<TextBlock.ToolTip>
<ToolTip>
<StackPanel Orientation="Vertical">
<Label>
<TextBlock Text="{Binding ElementName=ListItem, Path=Text, Converter={StaticResource ConvertItemToTitle}}"/> <!-- Item Title -->
</Label>
<Label>
<TextBlock/> <!-- Item Description -->
</Label>
</StackPanel>
</ToolTip>
</TextBlock.ToolTip>
</TextBlock>
</DataTemplate>
</ListView.ItemTemplate>

ToolTip, like Popup, is not part of the main visual tree so neither ElementName nor RelativeSource binding will work beyond ToolTip but DataContext inside ToolTip should still be the same as for ListViewItem
<ToolTip>
<StackPanel Orientation="Vertical">
<Label>
<TextBlock Text="{Binding Path=., Converter={StaticResource ConvertItemToTitle}}"/>
</Label>
</StackPanel>
</ToolTip>
Text="{Binding Path=.}" should give you same result inside ToolTip as in DataTemplate

Bind to Parent Object Property with RelativeSource

I've built a WPF based Treeview with
Item
-Subitem
If Subitem is selected, I would like to display also Properties of Item.
<StackPanel Grid.Column="2" DataContext="{Binding ElementName=myTreeView, Path=SelectedItem}">
<TextBox Text="{Binding Path=Name, Mode=TwoWay}" />
<TextBox Text="{Binding RelativeSource={???} Path=Name, Mode=TwoWay}" />
</StackPanel>
I guess I need to use a RelativeSource statement, but not quite sure how to do so.

{Binding RelativeSource={RelativeSource AncestorType={x:Type typeOfAncestor}}, Path=Name, Mode=TwoWay}

JesseJames has given you the correct way to use RelativeSource but the best you will be able to do with RelativeSource is bind to the TreeViewItem itself, which is just the container for your data object i.e ViewModel, meaning you won't be able to access your data objects properties(easily).
I think in this case binding to the container object would break the View-ViewModel approach you are using. Your best bet would be to create a Parent object within your ViewModel and bind to that object. So that now each object in your collection has a reference to it's parent which can now be bound to directly.
<StackPanel Grid.Column="2" DataContext="{Binding ElementName=myTreeView, Path=SelectedItem}">
<TextBox Text="{Binding Path=Name, Mode=TwoWay}" />
<TextBox Text="{Binding Parent.Name}" />
</StackPanel>
Also note that the SelectedItem property returns your data object and not the container.

I looked at your code, try binding simply to Name. It appears that your data context should already be set to the TreeViewItem due to the following line: <StackPanel Grid.Column="2" DataContext="{Binding ElementName=myTreeView, Path=SelectedItem}">. The RelativeResource binding is probably looking further up the logical tree and that's why your binding is failing.

Accessing ItemsSource source item

I'm creating an error list control similar to the in Visual Studio. Each error is represented by a class with three values: type (enum: Error/Warning/Message), text (string) and time (DateTime). The class has also two more read only getters: TimeString (returns time as HH:MM) and Icon (returns icon path based on type).
I have an ItemsControl bound to an ObservableCollection of objects via ItemsSource property.
I now want to implement a context menu for each of the items with two actions: Copy to clipboard and Delete from list.
How can I access the original item from the collection from the context menu item click handler?
Here is my XAML code:
<ItemsControl Name="itemsControl" ItemsSource="{Binding Items, ElementName=ConsoleWindow}">
<ItemsControl.ItemTemplate>
<DataTemplate DataType="Console.Items">
<Border Name="itemBorder" BorderBrush="LightGray" BorderThickness="0,0,0,1" SnapsToDevicePixels="True" Padding="4">
<Border.ContextMenu>
<ContextMenu>
<MenuItem Header="Copy to clipboard" />
<MenuItem Header="Delete" />
</ContextMenu>
</Border.ContextMenu>
<DockPanel>
<Image Width="16" Height="16" Source="{Binding Icon}" Margin="0,3,4,0" VerticalAlignment="Top" DockPanel.Dock="Left" />
<TextBlock VerticalAlignment="Center" TextWrapping="Wrap" DockPanel.Dock="Left">
<Run Text="{Binding Text}" />
<TextBlock Foreground="Gray" FontSize="9">
<Run Text=" (" /><Run Text="{Binding TimeString, Mode=OneWay}" /><Run Text=") " />
</TextBlock>
</TextBlock>
</DockPanel>
Thanks for any help

The DataContext property of any of the FrameworkElement derived elements (i.e. the TextBlock or Image or MenuItem) in the DataTemplate should have the original data item (the child automatically inherits the datasource of its parent unless otherwise set).
As part of the click event handler you get the element that is the source of the event, so cast it to MenuItem and check its DataContext property.

#slugster's answer would work. A more WPF-esque way of doing this would be to use a command for each menu item and set the parameter to {Binding}. WPF comes with commands for copy and possibly delete, so you might reuse those.