I don't even know such word "innit"...
It's (mostly London) slang, it means many things, depending on how and where you use it in the sentence, for example:
Yeah (omg innit, that girl is so buff!)
I agree (Do you have a sweet tooth? Innit, but I like cakes more than biscuits lol)
It's/that's true (Are you really 32? Haha innit, but I don't look it :) )
(Do you) understand? (Don't look at my girlfriend or I'll mash you up innit)
Aren't you (you're bit of a battyboy innit)
Isn't he/she (see that guy with the pink jacket, he's a battyman innit)
Shouldn't they (maybe someone should sort out that faulty speaker innit)
There are many more, but I have to go.... innit ;)