I have watched unforgivable blackness and read the book Papa Jack Johnson and the era of white hopes. However I don’t think it was mentioned who was Johnson’s trainer? I know choynski showed him somethings but I know other people besides Choynski had to help him come up with that style. For that era of boxing Johnson seemed to have the perfect style it was like he was a five steps ahead of the competition.
I think Johnson had several trainers and managers throughout his career. Abe Arends, John Connors, Sam Fitzpatrick, Tommy Flanagan, Morris Hart, Al Mclean, and probably others. I know that Joe Choynski trained him earlier in Jack's career. I'm not sure how long he stayed with Jack. I'm thinking that, after Choynski left, Jack pretty much trained himself, but that's just a guess.
Once he got to a certain stage, Johnson trained Johnson, whether he did or not. As Dundee put it about Muhammad Ali, "if you had an idea, better make sure he thought it was his idea." Hence the high turnover!