Who is the "doctor" that speaks to the judge before the hearing? What does our

knowledge about him say about Ponyboy and the hearing?

The doctor is a psychologist. Our knowledge of him informs us that Ponyboy is in a state of psychological distress which may indicate psychological problems, moreover, we can see that the audience has the function of judging Ponyboy's psychology based on what the doctor says about him.

Explanation:

The doctor is a psychologist responsible for assessing the condition of the condition that Ponyboy is in. That's because Ponyboy is shaken and very depressed after a crime led to Johnny's death. In addition to having a very delicate psychologist, he is disturbed and in denial about everything that happened.

The audience needs to have a diagnosis of Ponyboy's psychology, so that it is possible to decide whether it is safe for him to live with Darry, or for the safety of everyone, it is best to leave them apart. For this reason, the presence of the doctor is necessary.