主干其实是：He has been waiting a long time.
第一层加工,变为反义疑问,He has been waiting a long time, isn't it?
第二层加工,将前面半句变为感叹句,对a long time感叹,what a long time he's been waiting,isn't it?
翻译,他等了很长时间,不是吗?