What does Nick speculate about when Gatsby looks at Daisy's child in surprise?

Answer: Gatsby is surprised when he sees Daisy's child, because he refuses to accept that Daisy moved on with her life.

Explanation:

The novel "Great Gatsby", written by F. Scott Fitzgerald, is about a man who wants to reunite with his former lover, a woman named Daisy.

When Gatsby and Daisy parted, Daisy moved on with her life. She got married and had a child. At the moment they meet again, her life is completely different. Gatsby, on the other hand, still hopes that their relationship can be restored. He loves Daisy, and, as seen in the story, is ready to do anything to have her back. The narrator, Nick, tells us how Gatsby throws parties, stares at the green light near her house, all in hope that she will notice him. In doing so, he fails to realize that both her feelings for him and she as a person have changed. This is why Gatsby is caught by surprise when he sees Daisy's child - a physical proof that his future with Daisy is unlikely to become true.