모라요 vs 모르겠어요
If I want to simply say "I don't know" without irritation, should I use 모르겠어요? Does 모라요 always carry a negative nuance with it to show some irritation or frustration?

Question

Answer

If you don't want to be misunderstood, you should say "잘 모르겠어요" rather slowly

몰라요 in a rude accent could mean:
Stop annoying me.
As if I would care.
Not a problem of mine.
It's all your fault.

Answer

I don't think not only 모르겠어요 but also 몰라요 doesn't carry a negative nuance.
but if you worry about that and say formally, how about add subject?

"나는" 몰라요. 
"저는" 모르겠어요.