If you are trying to get a better sense of the company and your chances of succeeding there, here are my three big ones:
1. What percentage of reps have hit quota in the past 18 months and are there any trends they are noticing when it comes to the sales process?
2. How strongly do they feel about their product's market fit? (ideally, check reviews, news articles, competitor info etc. and be prepared to use that info when asking the question)
3. Ask who will be managing you directly and if you can meet them in a less formal setting 1-2-1 (if they're not already interviewing you)
If you're trying to ask questions to boost your chances of getting the job, depending on the culture and how much of a boiler room it is, you might be expected to close them. In which case, you should always ask whether or not they have any reservations, doubts or immediate feedback about you that you can clarify with them right there in that moment.
If not, you can crack a joke about how you'll expect to hear back from them very soon with a very generous offer in tow.
Before the very end of the interview you should take a moment to ask them if you've answered any lingering questions they have. If you know you have a weak point (weird employment gap, lack of experience, etc.) you can bring it up yourself. Get them to tell you what their biggest concern is right then and there and be ready to back it up. You want to make sure that anything that was "bugging" them was brought up and you were able to answer it.
Regarding actual end of the interview, I feel the best possible question is "In the past, what did other new hires do to succeed quickly?" or "What will be used to measure my success in this role at different periods of time such as 3 months, 6 months, or 1 year?"
This shows you plan to succeed and want to know how, and it also ends the interview with them thinking about you in a positive light. Framing the question that way naturally leads to them combining you and success as a part of the same idea.