HT1920: Recovering a forgotten iTunes Store account nameLearn about Recovering a forgotten iTunes Store account name
If you have a rescue email address (which is not the same thing as an alternate email address) on your account then the steps half-way down this page will give you a reset link on your account : http://support.apple.com/kb/HT5312
If you don't have a rescue email address (you won't be able to add one until you can answer your questions) then you will need to contact iTunes Support / Apple in your country to get the questions reset.
Contacting Apple about account security : http://support.apple.com/kb/HT5699
When they've been reset (and if you don't already have a rescue email address) you can then use the steps half-way down the HT5312 link above to add a rescue email address for potential future use