A photographer captured two pages of Mark Zuckerberg’s notes for his appearance at a Senate hearing on Tuesday. Once highlighted on Twitter, the image was retweeted thousands of times.

To many commenters, the paradox was clear. On a day Mr. Zuckerberg, the chief executive of Facebook, faced lawmakers’ questions about whether his company adequately protected users’ data, he experienced a disclosure of his own.

The talking points gave a detailed view of Facebook’s extensive preparations for the appearance before Congress of its billionaire founder. While some of the notes matched what he said on Tuesday, others reminded him what not to say or anticipated questions that were not raised. Mr. Zuckerberg will appear Wednesday for another day of testimony.

One section of the notes suggested responses in case Mr. Zuckerberg was asked if he would step down. He was not asked that question, but the suggested reply indicated he planned to stay.