In an InventoryClickEvent listener, if you do:

e.getClickedInventory().getHolder();

You get a wide variety of results depending on the block clicked that do not seem consistent:

• Smoker - org.bukkit.craftbukkit.v1_14_R1.block.CraftSmoker
• Chest - org.bukkit.craftbukkit.v1_14_R1.block.CraftChest
• Brewing Stand - org.bukkit.craftbukkit.v1_14_R1.block.CraftBrewingStand
• Dropper - org.bukkit.craftbukkit.v1_14_R1.block.CraftDropper
• Hopper - org.bukkit.craftbukkit.v1_14_R1.block.CraftHopper
• Minecart Hopper - CraftMinecartHopper{inventory=org.bukkit.craftbukkit.v1_14_R1.inventory.CraftInventory@1f2}
• Stonecutter - null on left slot, CraftPlayer on right
• Crafting Table - CraftPlayer
• Cartography Table - null on all slots
• Anvil - null all slots
• Loom - null left slots, CraftPlayer right slot
• Grindstone - null left slots, CraftPlayer right slot
• etc.

It looks like some of the 1.14 blocks do not give block references, and also the Anvil too.

Test plugin:

public class Test extends JavaPlugin implements Listener {


    @Override
    public void onEnable(){
        Bukkit.getPluginManager().registerEvents(this, this);
    }


    @EventHandler
    public void onInventoryClick(InventoryClickEvent e) {
        Bukkit.getLogger().info("DEBUG: you clicked on " + e.getClickedInventory().getHolder());
    }
}