About Apple ID security questions
Click here --> https://support.apple.com/HT201363 to "Learn about Apple ID security questions, including how to set up or change your questions."
"If you forgot the answers to your Apple ID security questions" click here --> https://support.apple.com/HT201485
If you see the message "not sufficient information" see if at this stage you can still sign up for Two Factor Authentication:
Two-factor authentication for Apple ID --> https://support.apple.com/HT204915
If you cannot resolve the issue by signing up for Two Factor Authentication, "Contact Apple for help with Apple ID account security"; click here --> https://support.apple.com/HT204169
There's some inconsistency here since if you need a verification code sent to another device you should not need to reset security questions. Two Factor Authentication instead of security questions. --> https://support.apple.com/HT204915 "With two-factor authentication, you don't need to remember any security questions. We verify your identity exclusively using your password and verification codes sent to your trusted devices and phone numbers. When you enroll in two-factor authentication, we keep your old security questions on file for two weeks in case you need to return your account to its previous security settings. After that, they're deleted."
If you didn't receive your verification or reset email click here --> https://support.apple.com/HT201455
If you are being sent a verification code to a phone number to which you no longer have access, click on the next link to see the various ways of getting a verification code and what to do if you cannot get one:
Get a verification code and sign in with two-factor authentication --> https://support.apple.com/HT204974 and a related new feature: Account Recovery Contact --> https://support.apple.com/HT212513
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