The River Pass #1
You'll find your first Raven in the area after Kratos and Atreus fall after crossing the bridge. Once you've cleared the area of enemies, look up at where the Projectile Draugr were to find this Raven.
The River Pass #2
After you pass through the large runic door and enter the cave beyond, you'll reach an area where the sky is visible. Look up and at the top of the rocks is a hard to see Raven, use the picture provided here for guidance.
The River Pass #3
In the clearing where you fight Brenna Dauði you will see some large rocks looming overhead, the Raven sits on top of one of these.
The River Pass #4
Once you reach the deserted village, look to your right before you drop down, the Raven is perched on the roof of the nearby house.
The River Pass #5
When you return to the Witch's Sanctuary to deliver Mimir's head to the witch, you'll see a chain leading to an upper path. Climb the chain and look on top of a ledge to your right to find this Raven.
The River Pass #6
When you return with the Magic Chisel and open the Hidden Chamber of Odin, take the elevator down and defeat the Valkyrie Kara. After the battle, look up to the south wall to find the last Raven.