Look for broad toe-pads on the gecko--if you see them, then he probably needs to be put into a high humidity tank. He could lose toes or tail tip if kept in a desert viv for long, and definitely will be seriously dehydrated. His weight and condition look good in the photo, but it is a small photo so hard to be sure. He looks like an arboreal gecko from here (should be a glass climber).

I'm not ready to say that is a Tokay. There are many other species of Gekko out there. I suggest posting the photo on a gecko-specific forum such as Geckos Unlimited or Gecko Resource Forums. You may get a better ID. This is crucial, because we could be wrong, and it could be some desert species we aren't familiar with--we can't see the feet in such a small picture.

I would say the first step is getting a real ID on the species. First, ask the friend where he got it, and take the photo to THEM--they can most likely ID it, even if your friend doesn't remember. Once you know the species, then look up care sheets. If the gecko really IS in an inappropriate environment, then yes, I think you should rescue it, and quickly. Obviously a rainforest species will perish quickly if housed in a desert. At the least, you can get it into proper conditions, and then if you don't feel up to keeping it long term, find a better home for it.