Question: Is it legal for a professor to ask me for a doctor's note or a copy of a medication being prescribed for a health issue that caused me to miss one class?
This is a good question but a tough one to answer. Most universities allow professors to set their own class-attendance policies. However, if your reason for missing a class is connected to a medical condition or disability, the professor cannot require a specific explanation of your absence (i.e., he or she cannot request the details of your health condition but can expect verification that your absence should be excused for health reasons). So, as you can see, there's some gray area here between what the prof can demand and what you should feel obligated to provide.