I am Bob....literally. I have been diagnosed with ADHD, I manage med free. I have always done very well in my career and in school, however, I also am intense for a lot of people. I do ask tons of questions, most are good, I am sure a lot are off in left field to some.
The way that works for me that I have learned with age & mistakes (I am betting I am "old" Bob versus your Bob), is write it down. I have been asked to not ask questions during a lecture or teaching. It's okay. You can do that. You can allow only very specific clarification questions pertaining to this exact moment, such as a word definition, or a further detail on an item, questions such as "Now is this before or after...". Just limit questions during the talk to things that need a "right now" sort of clarity. But all other questions should be jotted down to be addressed at the end of the talk. I can't speak to whether Bob is self-aware enough to know he does this, so there are 2 ways to approach that. If you think you can kindly address him alone on this after a class, then that is fine (I've had it happen to me & I felt bad I put the teacher in the position to have to do it, but wasn't offended). Or you can simply tell the whole class that you are having some trouble squeezing in everything that needs to be covered, so due to time crunch, from here forward, this is the format. If Bob persists after telling the whole class, you will have to tell Bob directly. His busy brain might have been thinking up a new question while you told the class. ;)
And FWIW if Bob asks a lot of great questions, you telling Bob they are great questions only feeds the cycle. It feels good to be told you have input to offer, even by way of questions & he might use that to validate that he is of value. He is a new hire and likely wants to be seen as eager. If that may be true, also hold off on complimenting the question. Your well meaning (and appropriate) compliment may, in fact, make the situation worse on the whole.