Early in the game after Link first visits Hyrule Castle, Doyle and the rest of the Carpenters can be found in North Hyrule Field. If Link speaks with Doyle, he talks about the sorcerer Vaati and how destructive he was. He references all the damages he did and it has caused a serious backlog of work for the carpenters.
For much of the game, Doyle can be found cutting lumber within a small hut at the southwest portion of Hyrule Town. If Link tries to speak with him then, Doyle will talk about the destruction that a lot of creatures have done, causing there to be a big rush to get things repaired.
Link is able to fuse Green Kinstones at various points in the game with Doyle. As it is a Green Kinstone fusion, it is not set to a specific treasure chest, but instead, one of the many possible treasure chests. There is one random Red Kinstone within the game that opens up a location in the Hyrule Castle Garden leading to a Piece of Heart, as well as a random Blue Kinstone that opens up a tree in North Hyrule Field leading to a Fairy Fountain. Doyle is one of the many characters in which Link can make this Kinstone fusion with.