Short for "
What are you doing now?"
BACKROUND INFORMATION:
Doni was a mistake made in an AIM
conversation. Instead of asking "
What are you doing?", the person decided to shorted it to "Doin?". But, they happened to make a mistake and type "Doni?". From that point forward they coined the phrase "Doni?", not ony becasue they were otaku and it sounded japanese, but just because it sounded cool.