Ok, no problem.

I haven't personally looked into either of these substances. I don't know of any controlled studies looking into these issues. I doubt that any have been done because people with AD/HD are considered high risk for drug abuse/dependence. It would be REALLY hard to get ethics approval for research like that. For any who might read this and not know - all research involving human subjects must be authorized by ethics boards. So, to give an AD/HD sufferer an illegal drug that some consider addicting would be a really tall order to accomplish.

Theoretically, neither substance is likely to be of much benefit. Nicotine can increase concentration, but the core problem for most AD/HD folks revolves around impulsivity (which adversely affects the performance of rote tasks). I don't think that pot reduces impulsivity much. Nor nicotine.