In life we are at some stage going to have to use the expression"I don't know", so as variety is the spice of life, using different ways to say “I don’t know” would make your conversation far more interesting and natural.
生活中我们常常会用到"I don't know"(我不知道)这个表达,可总这样说似乎让生活少了点情趣,用其他的表达来表示相同的意思会让你的话更加有趣和自然。

1. Dunno

This word is used informally and in spoken language, especially by teenagers who don’t want to answer their parents!

e.g. ‘When do you have to submit this essay?’ ‘Dunno. I can’t remember.'

2. I have no idea/I haven’t a clue/I haven’t the faintest idea

These expressions are used when you have no information and you cannot guess the answer to a question.

e.g. ‘What time does the film start?’ ‘I have no idea. Why don’t you call the cinema?’
例句:“电影什么时候开始?” “不清楚,你为什么不打电话问电影院呢?”

e.g. ‘Would you by any chance know where St James’s Street is?’ ‘I haven’t a clue. Sorry.’
例句:“你知道圣詹姆斯大街在哪儿吗?” “不好意思,不太清楚。”

e.g. ‘Could somebody please explain how this happened?’ ‘I haven’t the faintest idea.’
例句:“有没有人能解释一下这是怎么回事?” “我也不知道。”

3. How should I know?/Don’t ask me/Search me

These expressions are used when you do not know something and you feel annoyed that someone is asking you about it.

e.g. ‘Who left this mess on the table?’ ‘How should I know? I’ve only just come home.’
例句:“谁把桌子弄得一团乱?” “我怎么知道,我才刚到家。”

e.g. ‘What time did she say she was catching her train? ’ ‘Don’t ask me. I’m always the last to know.’
例句:“她什么时候说她在赶火车来着?” “别问我,我总是最后一个知道的。”

e.g. ‘Why didn’t he ask you for the keys?’ ‘Search me. I’m not a mind reader.’
例句:“为什么他不问你要钥匙呢?” “不知道,我又不会读心术。”

4. Who knows?/It’s anyone’s guess

These are used for saying that you don’t know something because it is impossible for anyone to know it.

e.g. ‘Will they ever find the missing aircraft?’ ‘Who knows? The search been going on for such a long time now.’
例句:“他们会找到失踪的飞机吗?” “谁知道呢?搜寻工作已经进行了这么长时间了。”

e.g. ‘How the situation will develop from here is anyone’s guess.’

5. Your guess is as good as mine

This is used for saying that you know as little about something as the person who asked you about it.

e.g. ‘Do you think we will be able to book the restaurant for Friday?’ ‘Your guess is as good as mine.’

6. Not as far as I know

We use this to say that something may be true, but you do not have enough information to know whether it is or not.

e.g. ‘Has Clive left the company? I haven’t seen him for ages.’ ‘Not as far as I know, but I haven’t seen him recently either.’
例句:“Clive离开公司了吗?我好久都没见到他了。” “可能吧,我也很久没见他了。”

7. It beats me

This is a rather informal expression to say that you do not know or understand something. “It” is often left out.

e.g. ‘Why did he do such a stupid thing?’ ‘It beats me’
例句:“他怎么会做这种蠢事?” “不知道啊”