Lens of Clarity lets you look at the top card of your library and at face-down creatures you don’t control whenever you want, even if you don’t have priority. This action doesn’t use the stack. Knowing what those cards are becomes part of the information you have access to, just like you can look at the cards in your hand.

Lens of Clarity doesn’t stop your opponents from looking at face-down creatures they control.

Lens of Clarity doesn’t let you look at face-down spells you don’t control on the stack.