Early in the game after Link first visits Hyrule Castle, Brent and the rest of the Carpenters can be found in North Hyrule Field. If Link tries to speak with Brent, he simply states that he is too busy. He needs to finish up his current project so that he can then repair the steps.
For much of the game, Brent can be found carrying lumber within a small hut at the southwest portion of Hyrule Town. If Link tries to speak with him, Brent will still say that he is busy and once against eludes to the steps that need to be repaired.
Link is able to fuse Green Kinstones at various points in the game with Brent. 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. Brent is one of the many characters in which Link can make this Kinstone fusion with.