It is never late to learn and today I present you some idioms about knowledge with examples:

to know something (somebody) like the palm of one’s hand
Example:
Believe me he’ll do it this way, I know him like the palm of my hand.
Everything that can be done is being done, you needn’t worry about that. Martin knows the place like the palm of his hand.

to know what is what
Example:
He isn’t such a fool as they took him for. He knows what is what.

to know the ropes
Example:
Mr. Bart said not to worry. And he’s smart. He knows the ropes.

Not to know what from which
Example:
I’ve been doing it the whole evening but still can’t understand what from which.

to get to know
Example:
‘Well, well’, he said, ‘we want to get to know our new friends, don’t we, Mother?’