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

{
  "type": "minecraft:crafting_shaped",
  "category": "redstone",
  "key": {
    "B": {
      "item": "minecraft:bookshelf"
    },
    "S": {
      "tag": "minecraft:wooden_slabs"
    }
  },
  "pattern": [
    "SSS",
    " B ",
    " S "
  ],
  "result": {
    "item": "minecraft:lectern"
  }
}