HT1920: Recovering a forgotten iTunes Store account nameLearn about Recovering a forgotten iTunes Store account name
Currently Being ModeratedDec 30, 2012 5:08 AM (in response to fireduck798)
If he has a rescue email address (which is not the same thing as an alternate email address) set up on his account then he can try going to https://appleid.apple.com/ and click 'Manage your Apple ID' on the right-hand side of that page and log into his account. Then click on 'Password and Security' on the left-hand side of that page and on the right-hand side you might see an option to send security question reset info to your rescue email address.
If he doesn't have a rescue email address then see if the instructions on this user tip helps : https://discussions.apple.com/docs/DOC-4551