Find out apple email id from iphone activation lock
How to find the AppleID

http://support.apple.com/kb/HT5625

If you can't remember your Apple ID, follow these steps to look for it:


  Go to My Apple ID (appleid.apple.com) and click “Find your Apple ID”.
  
  Enter the first name, last name, current email address, and any prior
  email addresses that you might have used to create an Apple ID. Apple
  uses this information to search for Apple IDs.
  
  If no Apple IDs are found, follow the onscreen instructions to create
  an Apple ID.
  
  If one Apple ID is found, choose whether to receive an email from
  Apple or answer security questions. Both options will conclude by
  asking you to reset your Apple ID password. Follow the instructions
  provided. 
  
  If multiple Apple IDs are found, select the one that matches your
  current email address. Then choose whether to receive an email from
  Apple or answer security questions. Both options will conclude by
  asking you to reset your Apple ID password. Follow the instructions
  provided.