In addition to Otto’s three, you can probably also technically count the episode where the whole town moves.
My all-time favourite: what is Sideshow Bob’s middle name?
Underdunk. 
Underdunk.
Continuing with the Sideshow Bob theme,
Who does consider hydrological engineering a “calling”?
The Phoenecians
Wasn’t it the Capodocians?
Yes, it was the Cappadocians (whom I’d never heard of).
Ah yes. The Phoenicians would have made too much sense.
Wait…what the hell is a Cappadocian?
From the same episode-
MA2: What crime does Krusty refer to during his concert, and where did it happen?
MA3: What does Krusty say that irritates the crowd?
MA2: He slugged some jerk in Tahoe
MA3: He’s just visiting Springfield Prison and gets to sleep and home tonight
That should be sleep at home, of course. I kid. I kid because I love. The best folk in the world are prison folk.
Apparently, Cappadocia is a region of Southern Turkey.
O3: One reason was for the “Simpson gene” that predisposes male members of the family towards low intelligence. Another was the crayon that a toddler Homer shoved up his nose. (Dr. Huxtable explained that in all the many times that Homer’s head was X-rayed before, he always held his thumb over the precise spot where the crayon was depicted, thus hiding it from view.)
O4: Marge was dispirited after Wiggums let the gang of counterfeit designer jeans dealers go for lack of evidence (while at the same time, all the men on the police force were wearing brand new - but suspiciously inauthentic looking - designer jeans.)
Q: From the same episode in which Marge becomes a cop, what magazine does Marge regularly read, and what new magazine grabs her attention?