Well, offhand, the AMS_AuditTrail table contains a list of all actions that take place in a particular application request. However, it doesn't appear that entries are inserted for when you reassign work.
It's possible in theory to capture this information by creating a table trigger to log to your own table whenever an UPDATE or INSERT or DELETE takes place on AMS_AppAssignments, however, that would be a bit of work.
I don't know if I would recommend going down that road, but Macrovision Professional Services could implement some sort of solution, and Macrovision Support would be able to log a feature enhancement request.