know somebody/something inside out
US /noʊ ˈsʌm.bə.di ˈsʌm.θɪŋ ˌɪn.saɪd ˈaʊt/
UK /noʊ ˈsʌm.bə.di ˈsʌm.θɪŋ ˌɪn.saɪd ˈaʊt/

1.
瞭如指掌, 非常熟悉
to know someone or something extremely well
:
•
She's worked here for twenty years, so she knows the company inside out.
她在這裡工作了二十年,所以她對公司瞭如指掌。
•
He's a local, so he knows this area inside out.
他是本地人,所以他對這個地區瞭如指掌。