Many thanks to Ayako for tweeting the link!
Tiger is in Los Angeles and has posted 3 photos with Keanu on his weibo page. The photos were of them training at 87eleven Action Design Studio. In the comment via the translator, Tiger said that Keanu was training 5-6 hr a day with no breaks for John Wick 2. It is not clear from the translation if Tiger is just helping out with the training or will also be in the film.
Update: Tiger is also on FB has also posted the photos there.