1. to know/learn something by heart 记住；背诵
I can recite this poem without looking at it. I know it by heart.
我不用看就能把这首诗背出来。我已经把它背下来了。

2. to know something like the back of one’s back 了如指掌
He's lived in this city all his life. He knows it like the back of his hand.
他在这座城市住了一辈子，对这里可以说是了如指掌。

3. know something inside out 了解彻底
She spent twenty years studying the history of London. She knows it inside out.
她学了20年的伦敦历史。对此，她已经了解的十分彻底了。

4. know next to nothing 几乎不了解；几乎一无所知
I'm really not interested in politics. I know next to nothing about it.
我对政治实在没什么兴趣，对此几乎一无所知。

5 .not have the faintest idea 一点都不知道
'Which is the longest river in the world?' 'I haven't the faintest idea.'
“世界上最长的河流是哪条河？”“我没什么概念。”

6. haven’t got a clue 一点不知道
'Can you tell me where Portsmouth Road is?' 'Sorry, I haven't got a clue.
“你知道朴次茅斯路怎么走吗？”“抱歉，我不知道。”