Where can you find out to whom a given Mac is registered?
The registration information that you enter when you setup OS X is stored in a hidden plist file in the system. 

That data is stored the file /var/db/.AppleSetupDone if you run the following command in terminal you should be able to see that information: 

sudo cat /var/db/.AppleSetupDone


This will show you the information entered. You will need to modify this information with a plist editor. For warranty claims Apple will know who registered the machine for AppleCare.