The Question and Answer section for Sir Gawain and the Green Knight is a great resource to ask questions, find answers, and discuss the novel.
You certainly can choose the codes of chivalry and to what extent Gawain adheres them. Gawain does a pretty good job. You might pick three codes of chivalry like honesty, purity, and never refusing an honorable challenge.
I would say honesty, honor, and purity.
I'm sorry, which specific section of the text are you asking about? If you're looking for a summary of the entire text, check out Gradesaver's study guide. You can access the study guide at the top of this page.