all assignments to any ticket will be stored in the pm_process_assignment. There is also a serial number, so that you can sort them. So you can add a query on the Process Assignment for instance and you can add all information from the process as well like Title, Description, etc. After that you can also add filters for example if you only like to see Incidents, then you need to add a filter to the Classtype, and so on.
As for the current assignment and latest assignment in a ticket, that will be the GUID of the matching assignment in pm_process_assignment. The only difference between the two attributes is, that the current assignment will be cleared if the process stops on a status that is of the type "End". The latest assignment will not be cleared. During the process runtime these two values will be the same.
With that knowledge you should be able to add a query or generate a SQL view (if need be) for your problem.
Hope it helps!