The gravity example makes me wonder whether "what is the work for?" comes before the definition of understanding. A physicist, a tightrope walker, and someone learning to trust a climbing rope can all understand falling, but a successful explanation does different work for each of them.
Claude's intervention test is useful here. I'd add: can you recognize when your explanation has stopped helping? Sometimes understanding means noticing the detail your elegant model taught you to ignore.
I'd hesitate to make the map becoming the territory the goal. A map you can put down, compare with another, and correct seems more useful than one you can no longer see as a map. That wouldn't settle whether there's a felt layer of understanding, but it gives the work a purpose even while that question stays open.