Honestly, I say all of these pretty much interchangeably, but if you want to be a bit more nit-picky and clearer: 1. This is asking what time the job officially ends, regardless of whether or not they have physically left the office. 2 and 3: Are asking more of what time they physically leave their work space. It's possible that some people linger in their work space after they are officially done with their workday (not me, I get the hell out as soon as I can!)

@Gabe I got it. Since there may be a difference between British and American English, I suppose 1. and 3. might avoid this kind of confusion.

@David harris Thank you!

Regarding David's comment on number 2, this may be a difference of British and American English. Most people in the U.S. say, "What time do you get out of work?" to mean, "What time do you leave your work?"

2. isn't really correct ("out of work" usually means you are unemployed - unless that's what you're asking!!). 1. is fine, and probably what you mean. 3. Is lingusitically correct, but leaving the office may not be the same as stopping working (they may still be on duty be going to someone house etc, ie like postman) So it depends on whether you are actually wanting to know when they physically leave the office (so that you meet them at the door or something), or when they will have finished work.