Why Hagrid said your cousin “don’t”, do he?

[Tienchutima]

From last scene of Harry Potter Hagrid said :
I know that, but your cousin don't, do he?

In which case can we (or must we?) use even with he, she, it?

Thank you very much

 

[lingobingo]

That quote is not standard English. It’s fictional dialogue written to emulate a local dialect.

It cannot be taken as an example of how to speak or write good English.

The normal way to say it would be:
I know that, but your cousin doesn’t, does he?

 

[S1m0n]

Hagrid is supposed to be lower-class and uneducated.

 

[Tienchutima]

I see! Thank you very much!