Q: I can't download Apple Music because I can't remember the answer to one of my security questions

If you have a verified rescue email address on your account (an additional/alternate email address is different) you can use that to reset them : If you forgot the answers to your Apple ID security questions

If you don't have a rescue email address you will have to contact Support in the country where you are (and which is therefore the country on your account) to get the questions reset - from the above link :

If you can't reset your security questions

If you can't send a reset email, don't have a rescue email address, or can't access email at your rescue email address, call us for help. When you call, you might need to create a temporary support PIN to verify your identity. After you reset your security questions, you might want to update your rescue email address.

If your country isn't on that ‘call us for help’ page then try this form to contact Support : https://www.apple.com/emea/support/itunes/contact.html

When they've been reset, and if you don't already have a rescue email address, you can then add one for potential future use

Or if it's available in your country you could change to 2-step verification : Frequently asked questions about two-step verification for Apple ID

You can change it by logging in Apple website