Conversation so far:
What is Kenneth, what is the frequency? from?
On October 4, 1986, while walking along Park Avenue to his Manhattan apartment, Rather was attacked from behind by a man who demanded to know Kenneth, what is the frequency?“
Was Dan Rather hurt while walking along Park Avenue on October 4, 1986?
As the assailant pummeled and kicked Dan Rather, he kept repeating the question.
Did Dan Rather find the attackers from October 4, 1986?
In 1997, a TV critic writing in the New York Daily News solved the mystery, publishing a photo of the alleged assailant, William Tager.
When did the Kenneth, what is the frequency? attack happen to Dan Rather?
On October 4, 1986, while walking along Park Avenue to his Manhattan apartment, Rather was attacked from behind
Why is the Kenneth, what is the frequency? question significant?
Tager claimed he thought television networks were beaming signals into his brain and wanted to find the frequency the networks were using to attack him, so he could block it.
Was the Kenneth, what is the frequency? question well known?
What's the frequency, Kenneth? became a popular-culture reference over the years

Question: Where was it referenced?
Self-contained rewrite: Where the Kenneth, what is the frequency?  referenced?