on which等于when或where,根据实际情境。
on which等于什么
关系副词都等于一个适当的介词＋which,在从句中作状语When=in/at/on/…+which;Where=in/at/on/…+which;Why=for/…+which
当“介词+which”在定语从句中作时间、地点和原因状语时，可以用相应的关系副词when,where和why来替换。这些都是定语从句里面由which引导的定语从句，介词提前。介词的使用除了意思上的区别，具体是要以which引导的从句而定的。
On Which怎么用
In which:在……里面；on which:在……的上面，或具体时间的某一天
On which和inwhich都可以用来引导定语从句，修饰先行词，区别在于介词on/in这取决于先行词的搭配
比如：
I can't forget the day on which we had a party.这个句子，先行词是day，原本的搭配是on the day.
I like the room in which there are many toys.这句话的先行词是room，词组搭配是intheroom。
on which与which的区别
on这个介词只是在动词需要时才用，并非固定。
例如：I don't know what the earth on which we live will happen.
这里主要是live需要，on which 一起做状语。
which就是一个独立的关系代词，直接作主语或者宾语。
例如：I don't like the book which is not interesting.这里which作主语。
in which, for which, on which, at which的不同用法
1、这些都是定语从句里面，由which引导的定语从句，介词提前。下面这些介词的使用除了意思上的区别，具体是要以which引导的从句而定的。
in which可以翻译成在……里面
The school（that/which） he once studied in is very famous.
= The school in which he once studied is very famous.
for which可以翻译成为了……目的
Tomorrow I will bring here a magazine （that/which） you asked for.
=Tomorrow I will bring here a magazine for which you asked.
on which可以翻译成在……的上面，或具体时间的某一天
I have a dresser in my bedroom, which there are many cosmetics on.
=I have a dresser in my bedroom on which there are many cosmetics.
at which可以翻译成在……里面或在……
The dumpling House which he often has dumplings at is very popular.
=The dumpling House is very popular, at which he often has dumplings.
2、当然第一点只是介词作为基本意思的用法，还有一些固定搭配，得具体情况具体分析。
The plane may be several hours late, in which case there's no point in our waiting.（固定搭配：in the case）
The speaker paused to examine his notes, at which point a loud crash was heard.（固定搭配：at the point）
Ten years of hard work changed her greatly, for which reason he could hardly recognize her at first sight.（固定搭配：for the reason）
The film at which I fell asleep was very boring.
（Here“at which”is based on“fell asleep at the film”因为电影无聊而睡觉。）
The little creature in which scientists are interested is known as ET.（这里“be interested in”是词组原因）
This is the book for which he is looking.（即等于This is the book which he is looking for，这主要是因为look for这一短语）
