Definition
To have extensive knowledge about a particular subject or activity, or to be exceptionally skilled at it.
對某事物瞭若指掌，非常精通。
She knows all there is to know about classical music; she can identify the composer of any piece.
她對古典音樂瞭若指掌，能辨認出任何樂曲的作曲家。
He seems to know all there is to know about every department of this company.
他似乎對這家公司的每個部門都瞭若指掌。
When it comes to computers, he knows all there is to know; nothing seems to stump him.
談到電腦，他簡直無所不知，似乎沒有什麼能難倒他。