Typically an Apple ID is an email address you have used.
Click on this link to read about ways to find your Apple ID --> If you forgot your Apple ID email address or phone number - Apple Support
or go directly to this link --> https://iforgot.apple.com/password/verify/appleid#
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."
Contact Apple for help with Apple ID account security - Apple Support
Also look in Keychain, and in a browser's security settings if you use it to automatically sign into Apple when using a browser.