Ask both the PI and others involved in the lab. If they don t match be careful. Both have their pros and cons so try and understand the benefits and drawbacks of each. Will you be able to attend classes, seminars, etc. Some labs are absolutely silent.
Some labs play music or the radio loudly.
I m interested in blank aspect of the research in the lab. Of course this is not an exhaustive list of questions to ask. The first questions help you understand what the PI sees as his role and what he expects from his graduate students. If your views on topics differ greatly from what the PI expresses, then you should be very careful about choosing that lab as a thesis lab. Your relationship with your PI is very important for the next steps in your career, and if you and the PI disagree fundamentally on your expectations, it is unlikely that you and the PI will have a good working relationship while you are in the lab.