You use whom after certain words, especially verbs and adjectives, to introduce a clause where you talk about the name or identity of a person or a group of people.
He asked whom I'd told about his having been away.
他问我对谁说过他不在的事。
You use whom at the beginning of a relative clause when specifying the person or group of people you are talking about or when giving more information about them.
One writer in whom I had taken an interest was Immanuel Velikovsky.
伊曼纽尔·韦利科夫斯基是一位令我感兴趣的作家。
You use whom in questions when you ask about the name or identity of a person or group of people.
who
'I want to send a telegram.'—'Fine, to whom?'
“我想发个电报。” “好的,给谁?”
Whom did he expect to answer his phone?
他以为谁会来接他的电话?