I am at the airport, waiting for my flight home after the first semester of my PhD. This time last year I was visiting prospective labs; for any anyone starting that process now I want to share questions you should consider asking prospective advisors and lab mates!
First, most important: Are you happy? This is a question for everyone you meet! You can ask more specific things like: Are you happy in this lab, in this department, in this city? People will be honest, and you can start to get an idea if you would be happy there.