There are things to do and not do in the quest for a more perfect exit interview process. Eric Cormier explains in a post for Insperity. He believes that face-to-face interviews are best, but it might not be the worst thing to combine a face-to-face interview with a written component. Among questions not to ask, remember that the interview is supposed to fixate on just the employee and the business, so avoid asking ugly questions about specific problem-colleagues’ performance, unless it is a direct supervisor who must be discussed. Cormier believes you should ask permission of the departing employee before any information discussed is shared with management, but frankly, I think that is going too far—what the heck is the point of the interview if the interviewer is forced to only vaguely paraphrase comments that were made? At any rate, do look for patterns that develop among leaving employees; this can be helped if a few (but not all) of the questions asked are standardized across the board.
For more, you can view the full article here: http://www.insperity.com/blog/how-to-conduct-an-exit-interview-the-right-way/