How did Ponyboy know that johnny recognized the socs in the park?

Ponyboy knew that Johnny recognized the Socs in the park because Johnny's reaction was one of fear and anxiety. When the Socs confronted them, Johnny's demeanor changed, and he became visibly tense, indicating that he was aware of the danger they posed. Additionally, Johnny's past experiences with the Socs, including a traumatic encounter where they attacked him, contributed to his recognition and fear of them.