Assuming you mean a math problem. I think, as a humanities bod, I'd think of "workings", but would think about whether I want to see their process (working?) or their raw materials (workings?).
I know both lazy and diligent students who do not submit work, to whom I might order, "Show your work." Especially if they were a photographer or artist.
To a lazy person whom I didn't want to get caught out - and to a colleague often accused of not being around enough - "Show you're working".
Edited at 2011-10-06 12:29 (UTC)