As far as the first two questions, if you have every worked at a health care facility, your training should have covered situations exactly like these. The hospital I work at has very specific protocols in place if someone is injured or if you see a coworker doing something wrong (how you report incidences, who to tell, etc). To me, these questions are not cases of ethics, but safety.
The last question is a matter of academic integrity. All schools have policies regarding cheating and dishonesty. Most of the time, if you do not report someone else, you are also violating the rules.
These questions absolutely have right and wrong answers. The problem with saying, "I would use my best judgement," is that your judgement leaves room for error and could lead to litigation.
A simple, "I would report the incident to my superior/safety reporting group/program director," will do. Or, "I would follow my institution's/company's protocol for this type of event." Do not waver. If you took any other course of action, you can bet you would be fired or dismissed immediately.
ETA: The thing is, it is not up to us to decide what is ethical. Our governing bodies (APTA, state gov't, school) have already done that. There is no gray area. It is all about integrity. Not following these laws and rules shows a lack of integrity.