Wiktionary
know someone
vb. (context idiomatic English) To have personal or social connections.
Usage examples of "know someone".
If he hadn't, they'd surely know, know someone had left by it, know what had happened.
If we know someone is guilty of war crimes, we must make a decision as to what to do with him.
If you know someone in the party who has a girlfriend, daughter, wife, mother, etc, make it this person), her hair is woven into a cage surrounding her and spun on the spear piercing her throat like thread on a spindle.
If you know someone is to be damned by their lack of faith in the Lord and yet do nothing to save them, are you not complicit in their damnation?