You will usually be asked at the end of the interview if you have any questions. The answer should be yes.
If the interviewer has repeatedly raised a concern during the interview, ask about that. For example, frequent questions about your long term plans with the company merit an inquiry about turnover rate.
If you can't think of anything to ask on your own, use one or two of these questions.
- Is there room for advancement?
- Does the company support ongoing training or education for the employees?
- What is a typical day in this job like?
- What is the company's/manager's management style?
- What is the company's mission statement?
- What's the next step in the hiring process?
Save questions about salary and benefits until you have been offered the job. It is also wise to not ask the interviewer for a critique of your interview performance. This puts the interviewer on the spot and makes everyone uneasy.