Programming has many various parts - graphics, game control (pathing, hits and other movement) - database structure and of course many other things.
I don't imagine in a short time I can become expert at everything. If however I spend more time on the things that would be needed - in a Score effort - then I could be of more use, faster.
It sounds like you mean "what would be most helpful if I wanted to contribute to a hypothetical project to create an emulator?" If that's the case, Lua is probably not the best place to start there in general. But if you want to contribute, and a hypothetical project were to materialize, and you specifically wanted to work on something Lua-based within the engine itself, I would imagine the proper place to focus your attention would be on studying Lua embedding techniques and Lua/C callbacks.
Alternatively, if you're thinking about contributing to such a hypothetical project by contributing Lua scripts themselves as part of the engine content I'd suggest looking at how another game (like WoW, say) exposes its Lua engine for practice.
