After completing the main story, you must speak to the hat in the desert land. Afterward, you can also find talking hats in the other worlds.
Sand Kingdom
At the southwestern entrance to the city, in front of a small group (right by the shop), you’ll find a sombrero with eyes. Talk to the hat for a Power Moon.
Metro Kingdom
You can find a hat in Metro Kingdom. He’s recognizable by his eyes. The man in question usually strolls from the main entrance park, along the eastern side of the main road, north towards the heliport and back again. Talk to him for a Power Moon.
Snow Kingdom
One of the residents at the Snowline Circuit track has an almost invisible partner: a Bonneter is hiding in his clothing; you can recognize him by the large eyes on his back. Talk to him!
Luncheon Kingdom
Behind the two shops in the food court, you’ll find a fork with a hat on it. Talk to the guy, and the finder’s fee is yours.
Mushroom Kingdom
Look for a Toad near the three trees in the northwest. You’ll find a hat with eyes on its head. Talk to it!