armor-statues/data/armor_statues/predicates/book.json

{
  "condition": "minecraft:any_of",
  "terms": [
    {
      "condition": "minecraft:entity_properties",
      "entity": "this",
      "predicate": {
        "equipment": {
	      "mainhand": {
	        "items": ["minecraft:written_book"],
		      "nbt": "{datapack:ArmorStatuesV2}"
	      }
	    }
      }
    },
	{
      "condition": "minecraft:entity_properties",
      "entity": "this",
      "predicate": {
        "equipment": {
	      "offhand": {
	        "items": ["minecraft:written_book"],
		      "nbt": "{datapack:ArmorStatuesV2}"
	      }
	    }
      }
    }
  ]
}