Hello, my father blocked his iPhone from mistake and he can't remember Apple ID, how can I recover it ?

Tell him to check his web browser autofill entries, the Keychain, and other records, or use Apple's iForgot service, or contact their Account Security team, or if you've encountered the activation lock, its original owner to click here and submit an unlock request.

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

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

Also look in Keychain, and in a browser's security settings if you use it to automatically sign into Apple when using a browser.

Both Niel and I recommended trying the I forgot service, and contacting Apple. Did you do both of those?