Final answer:
Daisy's confirmation of her engagement surprises Gatsby, contrary to his expectation of her denying it, which would likely be conveyed through a look of disappointment or confusion as described by Nick.
Step-by-step explanation:
When Daisy tells Gatsby, "Well, she does," upon being questioned about her engagement, it catches Gatsby off guard because he was expecting her to deny it. Gatsby's reaction is not explicitly stated in the context provided, but typically, Nick describes Gatsby's expressions very keenly throughout The Great Gatsby, often noting the hope, anxiety, and intensity in his demeanor. Nick would likely have described Gatsby's look as one of surprise, disappointment, or confusion, given Gatsby's expectations and the sudden deviation from his romantic ideals.