Talk to the fortune-teller and ask for help. Sometimes you may need to progress through the main story to see some events.
It is an item found by a trade quest.
You will get a stone slab from a magician.
You will need to give that to a fisherman so he will give you a fish.
You will give the fish to a cat found at the central plaza - you will get a shoe.
You will give the shoe to a toymaker, and he will give you a crystal ball for the fortune-teller.