I think if you have to write it, then "divvent knaa" would be okay, but an even more phonetic "divvent naah" might read easier. And sometimes it's worth trailing through the phonetics to figure out the puzzle - I think it must come down to how familiar the accent is to the person, so they realise the phonetic sounds they are reading are turning magically into an accent, mainly because it worked superbly for me as a reader in The Bridge by Iain Banks, where the accent was Glaswegian, but didn't work at all in The Book of Dave by Will Self, where the accent was cockney.
I'd certainly recommend a look at the bridge for how this can be used to the extreme - only a few chapters mind, but you'll spot them immediately. And oddly enough, some of the strongest scenes in the novel - and the parrot being one of his most memorable characters