ArcGIS Pro 2.7 API Reference Guide
MapURI Property (Bookmark)
Example 

ArcGIS.Desktop.Mapping Namespace > Bookmark Class : MapURI Property
Gets the unique path of the map in which the bookmark belongs.
Syntax
public string MapURI {get;}
Public ReadOnly Property MapURI As String
Example
Find all bookmarks associated with a particular map.
public IEnumerable<Bookmark> FindMapBookmarks(List<Bookmark> bookmarks, Map map)
{
  //Return all the bookmarks from a collection that are stored with a given map.
  return bookmarks.Where(b => b.MapURI == map.URI);
}
Requirements

Target Platforms: Windows 10, Windows 8.1

See Also

Reference

Bookmark Class
Bookmark Members