I generally ask candidates what they did last week at their existing job, and then ask questions about how they solved specific aspects of that particular job.

I generally ask candidates what they did last week at their existing job, and then ask questions about how they solved specific aspects of that particular job. If the person says "we built real-time tracking for our in-house vehicle fleet", I will just probe further and further about what role they played and how they went about the specific implementation details. If there is any kind of secrecy surrounding their work, I will simply offer them insight into what they'll be tasked with during their first week and ask questions in a similar manner. I'm not sure what advantage any other approaches have - I am hiring to fill a particular position. It's quite likely that the candidate will be in a similar position, so either I ask them about their current work and how they went about it, how they intend to accomplish the work assigned to them when they work with me.