The first Jotnar shrine can be found during the first mission in God of War.
Scattered throughout the world of God of War are Jotnar shrines, monuments left behind by the Giants that tell of stories from their history.
Finding all of the Jotnar shrines in God of War rewards you with lore, but also some experience to help increase the potency of Kratos and Atreus’ skills.
A fourth Jotnar shrine can be found during the mission, The Light of Alfheim.