der Wissensvorsprung, der Informationsvorsprung — a lead in knowledge, a lead in information. The Duden example sentence reads: Die Leserinnen und Leser unserer Zeitung haben einen Wissensvorsprung gegenüber anderen. “The readers of our newspaper have a lead in knowledge over others.”
das Insiderwissen — insider knowledge, which only an insider can acquire
der Geheimtipp — a secret tip, passed on personally by someone in the know
eingeweiht sein — to be initiated, to be in on it
wissen, wo der Hammer hängt — to know where the hammer hangs, to know exactly how things work
Ich weiß was, was du nicht weißt. — I know something you don’t know. A children’s taunt.