It might be possible security questions are not set in WHMCS. You can add security questions in WHMCS by going to the following path
WHMCS admin > Setup > Others > Security Questions
if you have added the security questions in your WHMCS and still unable to get these on cart page then it might be possible you have created API credentials in WHMCS and not gave permission of Decrypt password to that API credentials. You can give Decrypt password permission by going to
WHMCS admin > Setup > Staff Managment > Manage API credentials > Go to your API associated role > Edit > System > check Decrypt password checkbox.