You have posted a good question about the figurative language here in Native Speaker. A symbol, of course, is something that stands for something else. There are many symbols in the novel. Let's consider a few important ones in turn in order to determine their meaning. In my opinion, the most important symbols are the ones that create the original suspense for the reader in the opening scenes:
Emotional alien. ... Yellow peril: neo-American ... Stranger/follower/traitor/spy.
In divorcing her husband, Lelia first lists him as an "emotional alien." We learn soon that this symbol for Henry has to do with the Parks' great tragedy: the death of an only child. Mitt is dead, and Lelia grieves; however, Henry struggles to show his own grief to Lelia. The Parks’ marriage is rocked by at least one obvious tragedy, the accidental death of their only child, Mitt, but flounders because of Henry’s inability to articulate his devastation in a way that Lelia can understand. He, meanwhile, struggles with the cultural and generational difficulties of language use.
Next, Lelia provides another symbol for Henry as "Yellow peril: neo-American." From the very beginning both Henry and Lelia notice each other as speakers of the English language. Lelia is "better" at it than Henry. Henry is the one listening closely. Lelia notices this and immediately pegs him as a non-native speaker. As the book progresses, then, the symbol becomes clear. Henry is a "yellow peril" to Lelia because he is Asian. Henry is "neo-American" because he is not native and new to both the country and the language.
Finally, Lelia provides us a third symbol for Henry that readers are forced to find the meaning for throughout the book: Henry as "stranger/follower/traitor/spy." This is the symbol that takes the reader the longest to figure out; however, it's not because the symbol is hidden. It simply involves us learning more of Henry's story. Because Henry learns to "use" language, he is eventually employed by Glimmer and Company, a company that focuses on espionage. How? Glimmer and Company creates its livelihood from spying on immigrants in the US, other governments, and international companies. Conspiracy is their stronghold. Henry slowly becomes their most useful operative inside the company. The symbol, then, becomes clear: Henry is a "stranger" (an ESL speaker) and a "follower" (of the espionage company) and a "traitor" (in that he covertly observes in order to convict) and a "spy" (in that he is reporting back to his superiors on what he observes against them).
In conclusion, please realize that all of these self-proclaimed symbols come directly from the early pages of the book in the list Lelia makes of all of her husband's flaws (and the reasons why she is leaving him). In exploring them, we put the entire book in context.