The second outing of Pete Ross happens in “Pete Ross’ Super-Secret!”, a story in Superboy #90 (May 1961). In it, Pete Ross continues to be a stand-up guy against bullies picking on “that drip” Clark Kent and then happens to discover that Clark is actually Superboy.
This is a bit of clever planning on the writers, since it now gives them a chance for Pete Ross to hide something from Clark in clever ways by helping Superboy out in adventures. Like that time he pretended sunlight reflected in his eyes, allowing Clark to change into his alter-ego.
This makes Pete the first non-superhero character to know Clark’s secret outside of his parents.