Typically an Apple ID is an email address you have used (it does not have to be an iCloud one, and in fact it is better if it isn't). If you are currently using a mobile device that is logged into your account, go to Settings and tap your name at the top.
Look in Keychain, and in a browser's security settings if you use it to automatically sign into Apple when using a browser.
This support article describes ways to find your Apple ID --> If you forgot your Apple ID - Apple Support
or go directly to this link --> https://iforgot.apple.com/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 support and service - Apple Support