You find Jiahto at Toto Lake, pondering a broken stone slate with writing on it.

Quest Location

You can start this quest during the Sidon of the Zora quest, by talking to Jiahto at Toto Lake, at 3405, 0882, 0400.

Find the Broken Slate

Go slightly east from Jiahto, then go slightly north along the shore of the lake, and you will find the broken slate covered with some sludge. Throw Splash Fruit at the sludge, then use Ultrahand to move the broken slate in place on the wall near Jiahto.