I know, it's not very likely, but I got an apple watch last month, and there is really no working geocaching app for the watch. It does not need to do much, just show a map of a 100m circle around me and an allarm once I reach a 50 meter zone of a cache.
The watch can't show a compass that easy, because it has not the required hardware for one, but a map would be quite helpful. Maybe there would be the possibility to link the orientation to the phone in your pocket, but realistically just a small map with your location and a straight line to the cache should be enough. Nice additional feature would be an alarm once you are close enough to save some battery on the phone.
If you just want the "proximity"-thing. You can turn on the proximity alert in the "normal" app. once you are within 50 meters of the cache, your iPhone will display a notification, so also your watch will display this notification. I use this for caches where I roughly know the way to it, to only pull out my iPhone when I reach the 50 meter radius.