In the same location as the project, you will notice a new folder called: Revit_temp. This folder is automatically created by Revit and if deleted, will be re-created. You should NOT put other content into this folder.
Within the folder in Windows Explorer, you will see something like this:
You may need to turn on the "Owner" column... Right click over another title and select "Owner".
In my example, mikel is currently in the model... If there is more than one person working on the model, they all would be listed.