
Rainman is the one. I had forgotten all about Judge Wapner. But I remember him answering Jeopardy questions.
from Wikipedia Encyclopedia:
Raymond Babbitt (Dustin Hoffman) was an autistic man who always had to watch Jeopardy! at 5:00 and got nervous if he thought he was going to miss it. A clip showed Babbitt answering a question about Shakespeare, demonstrating his immense knowledge of the playwright and his works.