Very interested in him at the moment but for some reason I have not been able to find any solid answers for these questions. Does anyone here know the truth?
Early scribes of Mongol empire were Uyghur. Even now Mongols in Inner Mongolia use Uyghur script. Gengis Khan has been in contact with some of Turkic tribes from early on. Some of tribes of his initial confederation were partially Turkic. That could mean at least familiarity with their language.