As soon as he comes back,I'll tell him when you will come and see it

宾语从句．

when you will come and see it ：你何时会回来看它．（相当于名词，作宾语）
因为是还没有发生的事情，用将来时，所以用will.~

As soon as he comes back,I'll tell him when you will come and see it
整句翻译：他一回来，我就会告诉他你何时会回来看它．

宾语从句

我尽快在他一回来就告诉他,你什麼时候将会来看这个.

这句话多半是会是在电话中说的,句中的He还没回来,you也还没来,所以用将来时.

when you will come and see it 是一个宾语从句 这个宾语从句应用一般将来时

宾语从句。
因为时态是将来时。

宾语从句。
因为时态是将来时。