1、可以先把它用简单句分述：
They are talking about the man 他们在谈论那个人.
I know the man.我认识这个人
The man works there.那个人在那里工作.
2、再把这三个句子分别两个句子合成定语从句
They are talking about the man whom I know.他们在谈论我认识的那个人
I know the man who works there.我认识那个在那里工作的人.
3、接下来再把这两个句子合起来
They are talking about the man whom I know who works there.
4、句中的 whom 和 who,听起来声音重复,不太悦耳,可以改写如下：
把 whom 改为 that：They are talking about the man that I know who works there.
省略作宾语的whom：They are talking about the man I know who works there.
需要注意的是要分清两个从句哪个是主要的那个是次要的,把主要的直接直接跟在先行词后,另一个次要的用分隔的办法写在最后.