Could I ask if the following three are all acceptable (both in ordinary speech and in tests): Everything is going well (90%)/ going on well (10%)/ going off well (0%).
But someone could ask, "How is the new job?" and the answer could be, "It's going on well". So the difference would be that when you ask about an activity (e.g. a job, or some specific activity") as opposed to your personal situation, "going on well" would be acceptable.