I dunno k
He’s telling you he doesn’t know and he’s not even trying. He’s just tired of being questioned like a detective.
'I dunno k' he said when his friend asked him 10 times where he put his phone
'I dunno k' he said after his teacher called him out for not doing homework
'I dunno k' he said when his brother asked him what he wanted for dinner for the 3rd time that week