Hmm. To be honest, I'm not really sure. There are probably individual researchers, but I don't know if there's anything like a research center specifically for Ghost Pokemon.

Oh, but there is a research lab in a place called the Ruins of Alph in Violet City. That's more for archaeology than the Ghost Pokemon themselves, I think, but that might be a place to start? The Ruins are actually where I saw some Yamasks in the wild.