怎么理解 what is it you want to do?分析下语法?

怎么理解 what is it you want to do?分析下语法?
答：我的理解就是,它是What is it that you want to do?这个强调句型的特殊疑问句之漏打了一个词that.
请看句子的变化过程：
I want to join the army.肯定句.我想参军.
就join the army 提问：
What do you want to do?你想干什么?《---You want to do what?
就句中的what进行强调：
It is what that you want to do.
一般疑问：Is it what that you want to do?
特殊疑问：What is it that you want to do?
译：你想做的（究竟）是什么?