Apple ID and Activation lock
How do I remove activation lock when I don't have proof of purchase or Apple ID info?
iPad (6th gen) WiFi, Cellular
Question marked as
You can't. Apple won't unlock the iPad without a copy of the purchase receipt with the serial number on it.
See if you can recover the ID/password. Use every email address you can think of.
Apple ID - How to find your Apple An iCloud e-mail address is an Apple ID.
If you forgot the Apple ID password, enter the Apple (iCloud) ID, and click Forgot Password. See if you can get a Rescue or Notification email option if necessary. Link to contact Apple Support at the end of the 2nd article.