The Script inside of the NPC

script.Parent.NPCTalk.OnServerEvent:connect(function(player)
	if not player.PlayerGui:FindFirstChild("NPCChat") then -- Checks if the player already has the gui. Put your gui name between the quotation marks to the name of your GUI
		local gui = script.Parent:FindFirstChild("NPCChat"):Clone() -- Change here too. Clones the gui
		gui.Parent = player.PlayerGui -- Clone the gui and put its parent to the player gui.
	end
end)