That’s a snap, daddy-o!
(Now I need a smilie snapping its fingers, but there isn’t one. Whenever you need a (particular) smilie, it’s not around.)
groooooooooooooooooooooooaaaaaan
Sorry but Matt Groening has answerd this through his characters Binky and Bart Simpson. For those that can’t wrap their brains around a rhetorical question the sound of one hand clapping is four fingers clapping against the palm in unison. Ommmmmmmmmmmmmm.
Terry Pratchett answered it, too. (At least, I think it was Pratchett.)
The sound of one hand clapping is CL. The other hand provides the AP.
RR
I thought the sound of one hand clapping is obvious, a simple principle of physics and nothing to do with the mystical East.
The sound of a normal clap is the result of the percussion of two hands brought together rapidly.
One hand clapping is a sort of “whooshing” sound as one hand displaces the air in a localised area.
There also a high-school boy’s masturbation joke about one hand clapping. I hope there was not a reference to that in the original column. I would have checked, but the OP left no link, and I’m too lazy to search the archives for it.
That’s one hand fapping 
Let’s not forget the link to Cecil’s column.
Surely that’d be three fingers?
I guess I’m the only other person that came up with this. I have been able to “clap” with one hand for years, albiet not very loudly. Hold out your right hand, palm up. As quickly as you can, close the hand with your four fingers slapping your palm, and then open again. If you can grip firmly enough, quickly enough, it will make a clapping sound.
Mike S.
in NH