Dunno is used in written English to represent an informal way of saying ‘don’t know‘.
Examples:
- I dunno, maybe he was just trying to ensure the job was well done.
- His friend asked, “What happened?” to which Mr Kennedy replied “dunno, must have been [too many] and run out of air”.
- Instead of talking about, ohhh, I dunno, fixing our damaged public health infrastructure, or putting people back to work, Trump produced a veritable cornucopia of blather.