Objective of this question is to gauge your experience and ability on process modeling. Process modeling is one of the most important skills for a business analyst.
So one can answer this question as follows (However it will greatly depend on the technique you used in your projects):
I have used process modeling in couple of my projects, I have been involved with as a business analyst. Even though I know UML and DFD modeling techniques, we used simple flow charts to model the processes as our customer wanted it that way. (You can, of course, choose to replace this answer with the techniques you are most comfortable with)
So, in the first project, which was a Loan application and approval system, we started by creating the top level context diagram (a DFD terminology) to showcase the modules of the system and the interactions amongst them. Next to that, we decomposed the modules to identify the key processes and modeled them using the flow charts. In this case, some of the steps at this level, needed further decomposition and hence we went to the next level of decomposition and at that level, we found it to be good enough to proceed to data modeling.
In case, the interviewer would like to dig deeper he/she may ask you to draw one of these diagrams and you should be in a position to do so.
If you would like to know more about Process modeling, you can watch this video to know more about it (It’s a recording of the webinar on Requirements modeling using UML)