The questions change all the time and they are by no means anything that you need to study or prepare for...the purpose of them is simply to see if you are able to effectively communicate via writing. If you are not, you won't be able to hide that, not on the essay and my guess is that your lack of language skills would also become evident in the interview.
I will humor you though. A few example essay questions are;
Who was your favorite professor and what characteristics did you admire from him or her?
What was your favorite class in undergrad and why?
Questions like those are what we were given and although they do alter them frequently, the questions always seem to require ambiguous, reflective answers.