What if someone has lost their iPhone and cannot remember the iCloud email how can they figure out their Apple ID

Typically an Apple ID is an email address you have used. If you are currently using a mobile device that is logged into your account, go to Settings and tap your name at the top.

This support article describes 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

There is no Apple ID lookup service. You have to discover it using resources you have. Look in Keychain, and in a browser's security settings if you use it to automatically sign into Apple when using a browser.

You’ll need to know at least one piece of information