Hello, I'm an American wanting to get an LLM from a University in Europe. I'd like to know if there is much demand for foreign LLMs in the States, and what specialization would be best to obtain for the LLM. Any help would be appreciated. Thanks.

Little demand as far as I know. Except some very specific law firms in NY or Washington where they do antitrust or securities law, or very narrow niches such as humanitarian law. Look in Martindale-Hubbell and check the lawyers at law firms in places you want to work, if you see several lawyers with a European diploma it's an indication that the firms would value such a training. But hey the experience is worth it for its own sake.