I'm a distance runner. Knee hurts. Should I stop?

Yes & get evaluated. Healthy distance training should not cause persistent knee pain. Stopping running is a temporary fix-symptoms likely to recur if you do not address the underlying issue. See a sports med doc: treatment should be active recovery that involves safe cross-training & physical therapy/rehab to address underlying strength/endurance/flexibility/core deficits, gradual return to running when pain free.
Rest. Yes you shld rest.