it's internet slang, stands for I don't know. Sort of similar to the noise most people make instead of saying i don't know.
-what are you doing tonight?
- iono
If you sound it out its supposed to sound like i don't know
"Iono if I can go to the party today"
Iono is an abridged saying for "I don't know". It does not originate with Homer Simpson lol. It is a feature common in Ebonics that follows the morphological & vocab structure of the Niger-Congo substratum.
1: Where did she go?
2: Iono
Another variation to this is "Ion" which stands for "I don't." Expl: Ion get it.