The exposition, when we think about the plot of a given work of literature, is the initial stage that introduces the main characters of the work of literature and the conflict that goes on between them. Therefore, we can say that the exposition of this excellent novel comes in the first chapter, when Kenny introduces us to, in his words, the "weird" Watsons, that consist of his two parents, his older brother Byron and his younger sister Joetta. Also, consider how in the novel the character of Byron is focussed on, depicting how, on the one hand he is capable of acts that are really cruel, yet on the other hand, he is a very sensitive and caring elder brother. Note how this is explored through the depiction of Byron as both bullying Kenny through Kenny's flashback to the incident of "snow torture" and also Byron presented as a vulnerable (if laughable) character whose Narcissistic tendencies have led him into a sticky situation with his lips stuck to the wingmirror.
Thus we are introduced to the main characters and some of the conflicts that will be explored at greater length later on in the novel.