well ok, the boy reporter, jimmy olsen is not a secret agent. he was just forced into spying on chloe. but enough of that as for lana.
there was one episode "promise" where lana was inside a room with a vault that chloe was trapped in. lana didn't know chloe was in the vault. when clark came in lana hid behind some shelfs with wine bottles and then witnessed clark using his powers. i'm so bad at explaining but here's a small clip from that episode of that very moment.