Kang's projectiles make it difficult for Reptile to get stuff on screen. Getting stuff on screen = Reptile's only way of getting in.
Vs Sonya, it's sorta the same. The problem lies, though, in the fact that Sonya's divekick is too dangerous and Reptile is ass at dealing with divekicks.
Jax...Idk...I'm kinda iffy on that tbh. In my experiences I haven't had trouble vs Jax. I need to play Jr.
Kitana is 6:4. Kitana can't d1 in this matchup all that well. Elbow punishes naked d1s that are blocked. And spit cuts off Kitana's projectile game too much. It's much more of a hassle for Kitana than you think.
I'll write more after I get home from work.