For your diorama of "The Pearl" by John Steinbeck, one great scene to depict would be when Kino discovers the pearl in the ocean. This is a pivotal moment in the story, as it sets the stage for the events that follow. You could create a diorama that shows Kino in his canoe, pulling the pearl out of the water. You could add details like the other boats in the background, the rocky shore, and the color and texture of the water.
Another option could be the scene where Kino and his family are trying to escape from their village, with Kino carrying the pearl. This could be a dramatic and visually interesting scene to recreate in your diorama, with details like the darkness of night, the village in the background, and the rugged terrain of the mountains.
Ultimately, the scene you choose should be one that speaks to you and captures your imagination. It should also be a scene that you feel you can realistically recreate in a diorama. Good luck! <3