As a collaborator on a custom list that’s shared with you, you can now view a list of all collaborators on that list. You can also use the custom list based on the can edit or can view access granted to you by the list owner.
To view a list of your collaborators:
Access your shared custom list and click on the Actions dropdown in the top right corner of the page.
Click View List Info from the dropdown.
From the List info box that appears, select View Collaborators to view a list of all the collaborators on the list as well as the list owner.