모르다 (몰라요, 모르겠어요)
You can always add 잘 to make it stronger.
I lived in Busan (that's where I learned my Korean), and there wasn't really a way to say that in the dialect. If there was, no one around me (students, teachers, family, etc) ever used it. A slang-ish way to say it would be 모르겠으 where you basically hold the "SS" sound for a longer amount of time with no actually ending vowel. I hope I helped! ^^ Good luck! Busan dialect is so much fun~