Is the expression "showed it what for" or "showed it one for"?

For some reason I thought the expression was "showed him one for" but someone I know just said "showed it what for". Which is it? I have also heard the idiom as "give it what/one for".

If anyone has a tip on the etymology I'm interested in that too.

The standard expression is Give [someone] what for. I think the other variants are all just mistakes or 'personal idioms', but perhaps someone will confirm if any of them really are normal in some region or dialect.

I agree with etymonline that the expression originated as a brusque reply to someone you've just assaulted, who says "What [did you do that] for?".

"I'll give you what for!" is often used in a context where the speaker (assailant) has every reason to think the other person knows perfectly well why he was attacked. It doesn't have to be in reply to anything at all.

It derives from an old joke...

person 1:"If he keeps it up, I'll give him 'what for!'"

person 2:"'What for?'"

person 1:"Because he deserves it!"

OED

The Oxford English Dictionary has this:

As n. phr. in the slang phr. to give (one) what for = to inflict severe pain or chastisement. Also, to show (someone) what for: to make him take notice; to show who is in charge.

Their first quotation is 1873 (for "give you what for") but I some antedatings.

"Give you what for"

Here's a pair of 1868 antedatings. First, Springdale Abbey (page 159, 1868) by Joseph Parker:

Spite of your melancholy wheezing, to which the hydropathic adder turns a deaf ear, he catches you a sharp rap on the back, and with a knowing wink at one of his co-bucketters, he says he will give you " what for."

Second, Secrets of the Turf; or, how I won the Derby (page 125, 1868) by Samuel Bracebridge Hemying:

I'm the master of the situation, and if you don't take your hook instanter, I reckon I'll give you what for with this bit of wood.”

"Show you what for"

I found some earlier antedatings for this version, the oldest in Wild Western Scenes: A Narrative of Adventures in the Western Wilderness (page 137, 1858) by John Beauchamp Jones:

"What did you do that for ?" asked Sneak, rising up and brushing the snow from his head, and face, his fall having broken the icy surface.

" You rascal, you ! I'll show you what for !" cried Joe, endeavouring to get at him again.

This shows it used as an angry response to someone asking "What did you do that for?".