1. I think it's good to know about the specific practice itself along with information about the dentist and his/her staff members. If the dentist you're shadowing has a website, browse through that and read up on their biographical information if they have one. See what dental school they went to, what their interests are, etc. That way you can get a feel about who they are as a person, and if you guys share a common interest, maybe you can bring it up to spark conversation. Or if you have a particular interest in the the dental school they went to, you can generate questions based upon that and ask.
2/3. Honestly, the dentist is too busy focusing on the procedure, checking in on the patients, and going from room to room to check on the hygienists' work that I find it hard to ask them certain questions I've been brewing in my head before I even started shadowing. They'll come naturally to you as you watch, so don't sweat it. If I'm curious about what procedure they're doing, what instruments they're using, what the difference between X and Y are and when to use them, I'll ask if the situation presents itself. I also ask the DA's and hygienists a lot of questions and actually have followed them around more than the general dentist herself because she moves around a lot. Your only job is to watch so don't worry
Besides, some dentists may not even enjoy having questions to answer during procedures and would rather have the environment quiet in order to stay focused. On the other hand, some dentists may be open to conversation and talk about the procedure and explain what they're doing as they go along which can open doors to asking questions.
