It begins on pg 197 paragraph 3 and ends on paragraph 5 of the same page. After babbling on about "The Duke's Manor" and never coming to any real point, Pratt addresses Lolita's use of crude language, but only after she deemed Humbert's verbal ejaculation of "Sex play" as civilized terminology. (p196, p6). She then proceeds to make herself look like more of a fool when she tells Humbert, who has a firmer grasp on the English language than most native speakers: "I am always fascinated, by the admirable way foreigners---or at least naturalized Americans--Use our rich language." (p197, p 1) She then proceeds to use the language in a flighty, disjointed way by providing, again, completely irrelevant information.
The most ironic, and funny bit when describing Lolita's transgression Pratt informs Humbert in an almost soothing tone "It is rather a jolt when Dolly, who looks like a little lady, uses words which you as a foreigner probably simply do not know or do not understand...Dolly has written a most obscene four letter word which our Dr. Cutler tells me is low Mexican for urinal with her lipstick on some health pamphlets which Mrs. Redcock..."and she goes on with more irrelevant information.
Nabokov continually plays with language throughout this novel, but is never more insulting than in this passage. He pokes fun at pretension and ignorance while injecting some of his own ahem..crude little tidbits. Nabokov's nimble wordplay is a pleasure and a pain. At times he seems to look down on the reader for lacking his agility, but he seems to allow more in the event of honest confession of intellectual defeat and not "faking it". The most contempt he has is empty, idle words. Every word in this passage was carefully selected to poke fun, to draw the perfect conclusion. It's tight.