The quote that best represents the main theme of "The Book of Unknown Americans" is:
"I spent a lot of time trying to find it in me, but usually I couldn’t. I felt more American than anything, but even that was up for debate. . . ." (paragraph 3)
This quote encapsulates the struggle of identity that many characters experience throughout the novel, as they navigate their lives as immigrants in America and grapple with the concept of belonging and what it means to be "American." It highlights the internal conflict and quest for identity that is central to the overarching narrative of the book.