When he will come back is not sure .
When he will come back is still a question .
When he will come back is the day after tomorrow .
I want to know When he will come back .
I don`t know When he will come back .
The problem is When he will come back .
No one knows When he will come back .
When he will come back makes us worried ,
When he will come back is makes no different to us .
When he will come back is when we will be set free .
主语从名
when he will go home is known.
It is not known when he will go home.
宾语从句
I don't know when he will go home.
时间状语从句
I saw him when he went home.
定语从句，修饰在主句中作状语的时间。
I was reading a story yesterday afternoon when I heard the knocking on the door.
主语从句 when he will go home is known.
It is not known when he will go home.
When he will come back makes us worried.
It remains unknown when they are going to get married.
宾语从句 I don`t know When he will come back .
I want to know When he will come back .
That depends on when he shall come back.
表语从句 The problem is When he will come back.
What I am worried is when he will come back.
同位语 I have no idea when he will come back.