(rhetorical) Indicates strong agreement with a preceding statement.

Alternative form of not know which way to turn

(idiomatic) retort to questioning about a person by a stranger, when one does not want to confirm or deny knowing or being the person.

To understand one's rank or status and behave accordingly; to act humbly.

(set phrase) To understand completely.

(idiomatic, vulgar) To be well-informed concerning a particular subject; to have a capable command of a particular area of expertise.

It is necessary to be informed in order to do the right thing in a given situation.

(chiefly upper Midwest US, informal) Used as a rhetorical question to confirm agreement, knowing or understanding at the end of a statement.

A rhetorical question asked to show that the person asking it neither knows the answer nor knows who might.

(idiomatic, vulgar, followed by a wh-clause) I don't know; nobody knows; it is unclear.