When did Kakashi ..

[nointro]

When did he begin suspecting that it was Obito behind the mask of Tobi?

 

[Seventh Sama]

When obito used kamui to negate his kamui snipe or something like that.

 

[Joon]

After encountering him during the Sasuke and Itachi fight, or after Naruto defeated Pain, or after the Gokage summit during Naruto and Sasuke encounter, or against Obito during the War Arc.

 

[Gerkak]

When obito told him kamui snipe won't work on him

 

[Pyro NB]

When obito used kamui to negate his kamui snipe or something like that.

When obito told him kamui snipe won't work on him

These

 

[Angelic.]

During the war when Tobi freaked out at him lol

 

[A$AP Wap]

he always knew

 

[Nick01]

After the kunai scratched his mask.

 

[Rikudou Tobi]

When Kakashi tried to kamui gedo mazou's neck and Tobi stopped it with kamui.