Is 20,000 euros net (after taxes) enough to live comfortably for a year in Palermo?

I have opportunity to live in Palermo, Italy for a year or 2 as a visiting faculty.

i will know what do you mean with "confortably"... but if u mean a normal lifestyle (not Ferrari, xclusive party, shopping in Armani or D&G store...) i can tell u: yep! u can live confortably also with the half of your amount.
Don't forget that the average salary in Italy for a non-specialized worker is about 900/1000 euros.

Yes comfortably for sure but not luxuriously.

Definitively. You can live confortably, not luxuriously, and you'd be better off than many Italian Families!!!

definitively, man. the three guys they already told you all you have to know.

Yes!
Ciao! :-)

Definitely. Just make sure your university doesn't try to tie you into any overpriced accomodation. You should be able to get a studio apartment for about EUR 400 per month, or a little bit more if you want a one-bedroom. Bills and deposit are extra. I find that when you teach overseas many schools will charge you through the roof for the accomodation they provide, whereas if you're willing to live out of a hotel or hostel for a week or two you'll be able to find something much cheaper (and nicer) on your own.