Upvote:2
B, C or higher number D gates (54+ if I'm not mistaken) in Schengen area. I flew to Rome on Delta and Alitalia flights operated by KLM from all three of them, and KLM has great flexibility in shifting gates around.
However if you have a flight operated by Alitalia, the only one I was on departed from C gates both times I took it. This is further confirmed by Wikipedia (credit to @pnuts for the link).