Jossik is the keeper of the Lighthouse west of Rellekka. He also runs The Lighthouse Store on the first floor of the lighthouse but players must finish the quest Horror from the Deep to access it. After you finish the quest, he will give you an empty god book of your choice but it must be one of the main gods: Saradomin, Guthix, or Zamorak.
Salvaged Prayer Books
Talking to Jossik about prayer books will open up an interface from which you can retrieve completed prayer books and missing prayer books. You can also unlock new prayer books for a one-off fee of 5,000 coins.
It is possible to get multiple copies of completed prayer books from Jossik for no cost. However, you may only retrieve one copy of incomplete prayer books.