How to pick a PhD topic?
You mentioned the problem: "It needs to be something new". That's not only highly unspecific, but also extremely hard to gauge by a prospective PhD student.

Sure, you can start reading articles/conference proceedings and try to find interesting questions (e.g., what these authors mentioned as open questions). But in my experience, you need to be working in a domain/field to really get an idea which questions/problems are interesting and worth-while to answer/solve. After all, the research the papers are based on is usually at least a year old and conferences proceedings aren't that much up-to-date. So the person who likely can tell you whether something is new is your adviser, if s/he is actively doing research. A good adviser, who is part of the research community (visits conferences, works with other researchers, does peer-reviews for journals and conferences) should know what the other researchers work on (and thus reduce the risk that you get scooped half-way in your thesis) and guide you where you can make a contribution.

If you really want to work with this adviser, one way would be to check his/her publications and look for interesting topics/open questions. You could go from there and state your interest and ask him/her for possible directions where you can take his/her previous research. While the work has to be new and it must be your work, in my opinion it really helps to have a content expert to get started and to get good feedback. After all, I would consider a PhD an apprenticeship, not something you should do solo.