To view the project members that a file or document is shared with, click on the icon on the file or folder and a pop-up will appear with the list. From this pop-up, you may also kick on the icon to share with additional members.
Users will need view and edit permissions in documents to view shared members. Depending on the settings of a user's project permissions, they may be able to view all document entities, or just a subset of them. Folders and files marked as public are viewable to any users with view access to the Documents section, so it will not have shared members.