Alright so today I started kickboxing and I'm working on jabs,cross,hooks and such. So I want to know what muscle should I work out to make them stronger
Push ups, pull ups, bench press, etc. Focus on building strength, not mass, as muscle mass is useless in that context.
Also...if the only thing you're practicing is kickboxing, you're not doing MMA, you're practicing kickboxing. Have you seen any MMA fight where it didn't end up in an aikido / jujitsu style standoff? Make sure your grappling skills are top notch, as otherwise, you're out of luck no matter how hard you can throw a right hook.
you want to strengthen your forearms, biceps, shoulders, and triceps. all muscles of your arms. but you would probably want to hit your forearms very hard because thats how Bruce Lee was able to hit very hard. I read that he was crazy about strengthening his foreamrs. they say if you grabbed his forearm it was like grabbing a bat