What are common questions in an interview for a faculty position (W2/W3) in Germany and who is part of the panel?
(my experience is in Computer Science, but I assume the following to hold true at least for the sciences in general)


  Which questions are commonly asked in an interview for a faculty position (W2/W3 professor) in Germany (German "Berufungsverfahren")


Your milage my vary, but classics are the following:


Questions that target how your research will fit into the current research strategy. Who can you collaborate with? What strengths of the program will you foster, which holes will you fill? Your goal here is to convince the committee that you are both, related to existing professors enough that you won't be the odd (wo)man out, and different enough not to be redundant.
Questions that target your teaching, most importantly which courses you could take over, which new courses you would introduce, and how these would enrich the current specializations and programmes. It's possible that they already have a concrete (set of) courses that they need you to teach, and then they may outright ask you if you would do that, and if so how.
Questions that target your funding acquisition plans. Which grants would you apply for initially? How much funding do you expect to be able to acquire? Are there any funds that you would bring with you? What group size would you expect to be able to maintain?
Questions regarding your package. You won't need to say a concrete salary figure at this point, but the committee will likely ask how many research staff you will ask for, and whether you have any particularly expensive other needs (e.g., a compute cluster, other equipment). Note that W3 professorships in Germany tend to be large, asking for at least 3+ staff as package to start negotiations with should be seen as normal.
Questions regarding your intentions w.r.t. this position. Would you be moving fulltime? Can you see yourself living in this place for the foreseeable future? Why is this position even attractive to you? The main point here is to figure out whether you just want to negotiate with your home (or some other) institution, which is incredibly common in Germany ("Rufabwehrverfahren").


It's also possible that you get some "content" questions regarding your research, but I think it's rather rare. Most importantly, note that the interview is not an exam - typically nobody will assume that you don't know how to do your research, but they will want to know whether you and your research are the best fit for their needs. This includes doing a fair bit of background preparation to figure out what their needs actually are. In a way, during a "Berufungsverfahren" you are pitching your detailed area of research as much as your person.


  Who is usually in the panel (dean, student respresentative)


This varies, but both the dean and a student representative are at least likely members. Note that "being present" is not the same as "having impact on the decision". In my experience, the number of people who actually make the decision is usually 2 or 3.