If GS implemented some sort of quiz it would work better if each question was multiple choice. For example,
1. What is a travel bug?
A. a type of insect that is often found in geocaches.
B. an ailment commonly cause by traveling between geocaches
C. a trackable tag that you attach to an item
D. something that is responsible for 10% of groundspeaks revenue.
If you answered D, it would respond:
Incorrect. The correct answer is C. For more information see the Travel Bug page.
The point of the quiz should be educational, not to test if someone knows all the answers. You can take the quiz several time in a row until you answered, say, 8-10 questions correct. Since you would always be told the correct answer to each question, the quiz itself will educate new users.
Good point about not having to retake the quiz until all the answers are right, and I like the idea of linking to the right answer. I still feel like a really broad quiz for learning purposes would be great. We can't really fault newcomers for not knowing all the rules, since there is a LOT of information available, and it can be difficult to know what is the most important information to seek out when you're new to something. The quiz would solve that. Even if you have a friend teaching you, they may not share ALL of the most important info with you.
Maybe rather than the extra step of an approval code, just requiring people to take the quiz (and being directed to the right answer if necessary) is enough. An approval code might make geocaching seem a bit elitist, but a quiz on it's own would still get the job done of helping new cachers be good at it.