英语高手

首先你得明白两个词的词性：
where 是个方位副词
which 是个疑问代词或者是引导连词。
where is my room?(adv)
which is my romm?(proun)
上面是单句，下面看从句：
He asked where we should go.是去的不确定的方位或者地点，而且在从句中充当的是个状语的成分，只能用where.
He asked me which color i like.
作为是一个疑问代词，而且有相对的固定的领域：颜色选择。从句和主句都却少一个宾语。疑问副词where是不能充当这个成分的。
在来看看你说的可以替换的情况：
前提要搞清楚：他们的替换只能在表示方位地点的时候才可以，而且是替代句子中的定语的时候才会出现：地点状语从句中，where 只能指一个模糊的地点，而which则有一个定向的限定区域，意思不近相同：
例如：
I didn't know where he lived in the village.
I didn't know in which village he lived.
再如：
where he comes from is a secret
which province/state he comes from is a secret.
定语从句中：
it is the shelf where i put my book.
it is the shelf on which i put my book.
就可以替换，意思只能说是十分相近而已