'Revision History' on documents can be found in the context menu under the Inspects and Views option:


If you are using the new Context Mode the revision history will be found here:
Enter on the 'revision history' and changes made to the document/item will be listed.
If no changes are logged, there will not be an options for revision history.
If you are using the new context menu - the selection will be gray with a message stating no revisions to show:
If you are using the new context menu - the selection will be gray with a message stating no revisions to show:
Nb: The 'new' context menu can be activated under your user profile.