You won't be able to add a rescue email address if you can't answer your security questions. If you can't reset the questions contact Support in the country where you are (and which is therefore the country on your account) and see if they can reset them for you : Contact Apple for help with Apple ID account security
If your country isn't on that page try this form to contact Support : https://www.apple.com/emea/support/itunes/contact.html