How can I link a smaller survey that would serve as “extra credit” to an already existing survey?
You can add a REDIRECT ACTION (https://help.surveygizmo.com/help/redirect-to-a-website) to the Thank You page of your survey. In your case, the redirect URL will be your “extra credit” survey. The REDIRECT ACTION also has a logic function which will allow you to control how the redirect is triggered.
Come back to Community if you have any more questions.