minecraft-assets/data/minecraft/recipes/writable_book.json

{
  "type": "minecraft:crafting_shapeless",
  "category": "misc",
  "ingredients": [
    {
      "item": "minecraft:book"
    },
    {
      "item": "minecraft:ink_sac"
    },
    {
      "item": "minecraft:feather"
    }
  ],
  "result": {
    "item": "minecraft:writable_book"
  }
}