They will likely give an example scenario and then ask for your opinion on it (what you think can/should be done to address whatever the issue is). This was the case for three of the interviews I had that included writing assessment portions (two of which were for counseling programs). I would say don't worry too much about the content because even if you're uncertain of what the "right" answer is, they should expect that you might not know since you likely haven't experienced that type of situation before. Usually they seem to be more concerned with your ability to write, and I feel this way because prior to all three writing assessments, I had the interviewers tell me to focus more on writing well than answering the question correctly.
