What platform are you running on? That is, do you have access to the underlying database server for DocuWare?
On version 6.11, on premise, I can go into the SQL Server database and check the fields:
and see who last viewed a document. I just viewed an old document and it updated those fields to the current date/time and my username.
Those fields also appear to be accessible via Platform SDK API queries as well as URL Integration, though I am not sure how you could expose them on a regular search dialog. What you could do is add a field of your own that uses a "Predefined entry" of "Access date" and "Access user" (short or long name). Then you could search by access date and access user. I do not think there is any other way to expose those system entries on a standard Search dialog.