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.
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.
3. know something inside out 了解彻底
She spent twenty years studying the history of London. She knows it inside out.
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.
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.‘
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.