ArcGIS Pro 2.6 API Reference Guide
ShowProperties Method
Example 

ArcGIS.Desktop.Layouts Namespace > Layout Class : ShowProperties Method
Opens the Layout Properties dialog.
Syntax
public void ShowProperties()
Public Sub ShowProperties() 
Exceptions
ExceptionDescription
This method must be called on the GUI thread.
Remarks
This method must be called on the GUI thread and not in the background using QueuedTask.Run.
Example
//Open the layout properties dialog.

//Get the layout associated with a layout project item
LayoutProjectItem lytItem = Project.Current.GetItems<LayoutProjectItem>().FirstOrDefault(item => item.Name.Equals("Layout Name"));
Layout lyt = await QueuedTask.Run(() => lytItem.GetLayout());  //Worker thread

//Open the properties dialog
lyt.ShowProperties();  //GUI thread
Requirements

Target Platforms: Windows 10, Windows 8.1, Windows 7

See Also

Reference

Layout Class
Layout Members