How to remove activation lock, when you don’t remember your Apple ID

If you forgot your Apple ID  - Apple Support

If you forgot your Apple ID password  - Apple Support

If you were the original purchaser and can prove it with

a receipt from Apple or Apple authorized iPad retailer showing

the serial number of the iPad, make a genius bar

reservation and bring in the receipt, iPad, and government

issued photo ID to Apple and they may assist in resolving the problem.

If the iPad was purchased used or there is no receipt, the AppleID and passcode must be recovered 

It is highly recommended that you make a Genius Bar Reservation to avoid delay at the Apple store

https://www.apple.com/retail/geniusbar/

Activation Lock page: https://al-support.apple.com/#/getsupport