I think ever since they were caught by the Kaido i mean literally all of them the red scarbbards and Oden, kinemon already knew rhat the traitor was Kanjuro but he refuse to belive it, and one by one the events that happend led him to really think that it was Kanjuro, first of all how they were caught by doflamingo? How the hell dofi knew about momonuske and how Kanjuro made stairs for people to get Viola and King riku, usopp get to where they at, even tho Kanjuro plans failed because of the straw hats i think Kinemon still doubts himself that it was Kanjuro, the only thinng that made him really think that it was Kanjuro was the events on Wano, because that time everything was serious. Because people died that was close to them just like Yasuie Imagine kinemon’s pain when he had to do his plan to make kanjuro appears that he was the traitor even tho just like Kanjuro, Kinemon also thinks that Kanjuro was his also his closest friend….