I'm native Japanese, and I like Joseph's both sample phrases. We tend to finish our sentence unclear, but it gives the speaker more options for her/his answer. In that sense, you could also say 3. お仕事は何を？ 4. お仕事はどんなことを？ The sentences above are incomplete, but they are commonly used. It's common to ask someone's job in a small talk, although if the speaker hesitates his/her answer, that's a good sign that you should change the subject. And one more - if you compliment what he/she does, the normal response would be "Oh, no, there's nothing good about my job" or "That's a boring job" and so on - but the real meaning is "Thank you." We are trained to be modest :) (I failed)

Yoke san, arigato gozaimasu.

Thanks a lot, Joseph.