I forgot my Apple ID on my iPad

Typically an Apple ID is an email address you have used.

Click on this link to read what to do "If you forgot your Apple ID" --> https://support.apple.com/HT201354

or go directly to this link --> http://iforgot.apple.com/

Also read about "What to do after [or before] you change your Apple ID email address or password" - https://support.apple.com/HT204071

If you still need help:

Contact Apple for help with Apple ID account security "This article provides country-specific Apple Support contact information for customers seeking help with their Apple ID password or other security-related issues."

https://support.apple.com/HT204169