If you don't know the answers, if the steps in the article below don’t work, contact Apple ID Support, although based on multiple posts I have read, they will not help you recover the answers to your security questions.
Apple ID - If you forgot the answers to your Apple ID security questions. *
From the article below.
Without proof of your identity via security questions and other carefully selected criteria, Apple Support can't help you reset a password or perform any other actions on your account. These policies are audited and reviewed on a regular basis.
Security and your Apple ID. *
Apple ID - Official Apple Support. -
Contact Apple for help with Apple ID account security - Apple Support. * (Link doesn't always load)
Get Support - Work through the screens to get a chat option.
Apple Support schedule phone call. -
Apple on Twitter
See if anything here helps.
Solution to the forgotten Apple ID security questions. -