Depending upon one's penchant for humor, there are many scenes that evoke laughter in Wilde's irreverent play. But, because the farcical appeals often to many students you may wish to choose such a scene.
In Act 2 the vacuous Cecily and the idiotic Miss Prism along with the foolish hypocrite Dr. Chausuble evoke laughter from the viewers/readers with their dialogue. So typically "Wilde-ish," Cecily speaks in unconscious contradictions, displaying the fatuity of the Victorian ingenue. In fact, the dialogue of this scene recalls the humor of Restoration Comedy, such as The Man of Mode.
In the opening scene, Cecily is not so naive that she does not know how to rid herself of Miss Prism [named after a silly character from Dickens] by telling Reverend Chausuble that her tutor has a headache and needs a walk. Chausuble says, Were I fortunate enough to be Miss Prism's pupil, I would hang upon her lips." When she glares at him, he attempts explanation, "I spoke metaphorically.--My metaphor was drawn from bees [the birds and the bees?] Miss Prism leaves Cecily to her German lesson while she takes a walk with the rector who has lascivious designs. As they walk, Miss Prism tells the minister he should get married. "A misanthrope I can understand--a womanthrope, never!" Chausuble, who is a scholar, shudders at the malaproprism. [the word should be misogynist] . Then she continues in this manner, "the very celibacy leads weaker vessels astray."
CHAUSUBLE But is a man not equally attractive when married?
MISS PRISM No married man is ever attractive except to his wife.
CHAUSUBLE And often, I've been told, not even to her.
MISS PRISM That depends on the intellectual sympathies of the woman. Maturity can alway be depended on Ripeness can be trusted. Young women are green. [Dr. Chausuble shudders]. I spoke horticulturally . My metaphor was drawn from fruits....
For the Victorian audience, the mention of bees and fruits are well known as euphemisms for sexual words. The "green," of course is suggestive of venereal disease, so Wilde is again having fun with his Victorian audience.
In the meantime, Cecily has a visitor who calls himself Ernest, but is really her Uncle Jack's brother Algernon; he poses as the erstwhile "friend" of Jack and introduces himself to her. But, before he enters, Cecily says to herself, "I have never met any really wicked person before. I feel rather frightened. I am so afraid he will look just like everyone else." And, when Algys/Ernest enters, she exclaims, "He does!"
After the rector and Miss Prism return, Jack appears and tells them that his friend Ernest has died in Paris. However, shortly after this, Algernon appears as Ernest! And the scene that develops after this is hilarious as the dramatic irony develops.
Of course, the final moment in which Jack is identified as the lost brother of Algernon and he is accepted by Gwendolen because he is of her social class, and his name is Ernest, the name of a husband she has so desired becomes another ridiculously funny moment and deeply satirical moment. When Lady Bracknell says "My nephew, you seem to be displaying signs of triviality," Jack delivers the most hilarious and line of all--"...I've now realized for the first time in my life the vital Importance of Being Earnest,"