So there I am, doing the Pride of Alkosh. I have managed to get the last stone of the third trial hopelessly wedged, stuck, immobile. Now what do I do?
Go back to where the stone came from; there should be a glow-y spot on the ground. Activate it, and the stone should teleport back to its starting point.
If that's inaccessible somehow, you can try leaving the area and returning; lI believe they'll reset. But you should generally be able to get back to a stone's starting point for a do-over.