You can use WHOHAS to track which users have certain drawing files open.

After you select a file, the ownership information is displayed at the Command prompt.
The information includes the current user’s computer name, login ID, and full name
(if available) and the date and time the drawing file was opened.

The information displayed by WHOHAS is stored in a temporary DWL (drawing lock) file.
A DWL file is deleted when the file is closed.