Who should you give your spell and incantation books to in Elden Ring?

gamepur.com:

While exploring Elden Ring’s open world, you’ll encounter many prayerbooks and scrolls that you can give to certain NPCs. In return, these NPCs will offer to sell you new sorceries and incantations that were not previously available for purchase. There are two NPCs that you can give prayerbooks/scrolls to: Brother Corhyn, and Miriel, Pastor of Vows.

You’ll first find Brother Corhyn in Roundtable Hold. At first, he’s the easiest prayerbook-accepting NPC to find, but as you progress in the main story, he’ll move to various locations across The Lands Between, such as Atlus Plateau, and Leyndell, Royal Capital. Given that he moves around a lot, we don’t particularly recommend you give all of your prayerbooks to him.

Instead, you should give all prayerbooks/scrolls to Miriel, a large, hat-wearing turtle that the Elden Ring community has come to affectionately know as “Turtle Pope.” You’ll find Miriel in the Church of Vows, which is located just northeast of Raya Lucaria Academy.

Miriel is the ideal choice because his location does not change. When you first meet him, he’ll admit that his legs “aren’t what they used to be,” and as such, he will always remain in the same spot. The only reason he’d disappear is if you killed him, and there is no benefit to be gained from doing that. If you get a new prayerbook or scroll, just take it to Miriel, and the Turtle Pope will be happy to teach you some new spells.