这两个词都既可以做疑问词引导
特殊疑问句，都可以做疑问代词和
关系代词引导从句。
一、做疑问词
who是
主格，只有名词性质
1）用于疑问
Who put that light out?谁把灯灭了？
Who told you so?谁给你说的？
2)用于修辞性疑问句
Who could blame you?谁能怪你呢？
Who would have thought of that?谁会想到这个呢？
which的用法：用于指物或人，有名词和形容词性质
1）This is my copy,which is yours?(单数，做定语）
2)Which of the stories do you like best?（单数，做宾语）
3)Which of you will go with me ?（单数，做主语）
二、1，做疑问代词引导从句
1）Who he is doesn't concern me.他是谁与我无关。
2) I don't know which one is ture.我不知道哪一个是真的。
2，做关系代词
1)Nobody who understands the subject would say such a thing.
懂这一行的人是不会说这种话的。
2）The river which was already well above its normal level.
河水已经超过正常水位。
3，who 和which主要在引导
定语从句中注意区别
引导定语从句的
关联词为关系代词和
关系副词who\which 都为关系代词，在从句中可以用作主语，宾语，定语等
who是主格，在从句中用作主语
whom 是
宾格，在从句中用作宾语
whose是
属格，在从句中用作定语
The man who was here yesterday is a painter.
I know the man whom you mean.
I'd like a room whose window looks out over the sea.
我想要一个窗户面临大海的房间
（whose 作定语，指room,可以用of which代替，of which较为正式）
which在从句中既可以做主语，亦可以做宾语，一般指物（在非正式问题中可以省去）
This is the book which has been retranslated into many languages.
这就是那本有多种译本的书（关系代词which用作主语）
Where is the book which i bought this morning?
今天上午我买的那本书在哪？(作宾语可省去）
以上内容希望能帮到你！