If it has Settings > iCloud > Find My iPad enabled on it then he will need the password of that account to reset it, either to turn off 'Find My iPad' before doing so or (if using recovery mode) after resetting it to then reactivate it.
If he can't remember his id : Recovering a forgotten iTunes Store account name - Apple Support and How to find your Apple ID - Apple Support
And to then reset the password http://iforgot.apple.com
If he can't find his id via either of those then you could try going to an Apple store if you have one nearby, or contacting iTunes Support online (http://www.apple.com/support/itunes/contact/) and see if they can/will remove the iPad from the account - they are likely to want to see proof of ownership before they might help e.g. original receipt with the iPad's serial number on it.
If he doesn't have Settings > iCloud > Find My iPad enabled then you should be able to reset it via Settings > General > Reset > Erase All Content & Settings (after copying off any purchases to his computer's iTunes library, File > Devices > Transfer Purchases, and any content that he wants to keep e.g. photos, documents).