In this brilliant satire by Washington Irving there are certainly any number of examples of humour to pick from. You might however want to analyse the presentation of Tom and his wife, and the kind of marriage that they "enjoy" to see a number of different incidences of irony and sarcasm and how it is employed for comic effect. First of all, consider the way in which the greed of Tom and his wife is described. So miserly are they said to be that they even try to cheat each other:
Whatever the woman could lay her hands on, she hid away; a hen could not cackle but she was on the alert to secure the new-laid egg.
This picture of Tom's wife constantly prowling around for anything she can find to stow away is one that is grimly satirical and clearly uses exaggeration for comic effect. Not, too, the way in which the skinny horse would "look piteously at the passerby, and seem to petittion deliverance from this land of famine." Again, the conditions in which Tom and his wife live are so bad that even the animals want to get out. Lastly, consider the way that the sounds of the squabbles between Tom and his wife made any travellers passing by profoundly greatful that they were unmarried:
The lonely wayfarer shrunk within himself at the horrid clamour and clapperclawing; eyed the den of discord askance; and hurried on his way, rejoicing, if a bachelore, in his celibacy.
Clearly we can see several examples of sarcastic humour therefore from the presentation of Tom and his wife and their marriage and living arrangements, which use exaggeration for comic effect.