表达 “know something inside out” 的意思是 “对某件事情、某个科目或主题了如指掌、洞悉透彻”。

例句
Don’t worry! You’ll be fine in tomorrow’s exam. You know the book inside out by now!
别担心！明天的考试你一定会考好的。你现在对这本书已经了如指掌了！

If you ever have any questions about the new IT system, ask Polly. She helped build it, so she knows it inside out.
如果你对新的信息技术系统有任何疑问，就去问波莉吧。这个系统是她帮忙建立的，所以她对整个系统了如指掌。

My grandad was a chess fanatic. You could ask him anything – he knew the game inside out.
我祖父曾是个国际象棋迷。你可以问他任何问题，他对这个游戏了如指掌。