The Quest is started from a hilltop that's surrounded by giant bones, with three glowing holes for spheres in the ground, by a small altar. To get there, follow the road north out of Lurelin Village, and then break away from the road to keep heading north around the various cliffs and hills. The Tawa Jinn shrine is located within the Faron region, specifically a fair way north and slightly west of Lurelin Village, or even further north-east of Faron Tower.
If you need help finding and solving other Shrines, our Zelda: Breath of the Wild Shrine of Trials locations page can help, while our Zelda: Breath of the Wild walkthrough and guide covers other aspects of the game. The challenge inside, named the Tawa Jinn's Blessing trial, is simply a reward for finding it, so you're bound to walk out a success.
Tawa Jinn is one of the many Shrines located throughout Zelda: Breath of the Wild, and is accessed via the Three Giant Brothers Shrine Quest.