Why would a job interviewer ask you about your future goals?

To judge whether or not you are a motivated person who aims to push yourself to your fullest potential.

Ireally don't know the answer

This sounds like a personal reflection on something you did. it is asking the hardest part, or a part you may have struggled with on an informal interview you must have done. it is also asking advice you'd give someone else for the process of completing an informal interview, so you should write something that would . for example, maybe the first thing they should do, something they should include.