For the undergraduate interns they mostly ask your opinion on various matters of European policy. Nodody expects you to know much but they want to see the ability to express your ideas and make sure you are easy to work with. The entire office is basically operating under a healthy "hire only teamplayers" policy and it is an important component of the hiring process. If you're selfpromoting or unpleasant you won't last long there anyway and they look for that in the interview.