The humorous phrase where did you get your licence?, usually followed by an incongruous supposition, is an allegation of incompetence addressed to the driver of a motor car by another motorist, or by a cyclist or a pedestrian.
—Cf. also the phrase what else did you get for Christmas?.

These are some of the occurrences of the phrase that I have found, in chronological order:

1-: From a letter published in the Daily News (New York City, N.Y., U.S.A.) of Sunday 16^th July 1933:

JUST IN PASSING.
While I was driving the other day, I attempted several times to pass a certain car. At last I succeeded in doing so. As I whizzed by I yelled out to the driver: “Where did you get your license? In a mail order house?” A week or so later, at a friend’s house, I was introduced to the person who had driven that car. He immediately scowled at me and said: “I want to inform you that I have been driving my own car for ten years, young man!”
GEORGE LANSPERY.
Route 1, Newburgh, N. Y.

2-: From the column On the Side, by E. V. Durling, published in the Pittsburgh Sun-Telegraph (Pittsburgh, Pennsylvania, U.S.A.) of Saturday 29^th November 1941:

“As cracks to be hurled at careless and stupid auto drivers,” writes a subscriber named Dorothy, “How about ‘where did you get your driver’s license; out of a grab bag?’” Not bad, Dot. But a little song. Brevity is the soul of auto traffic repartee.

3-: From a letter published in the Sunday Dispatch (Pittston, Pennsylvania, U.S.A.) of Sunday 23^rd November 1947:

MUD SPLASHER SMEARS DURYA CHEER LEADERS
Editor,
Sunday Dispatch
This refers to the person who has less brains than a child for passing out the Durya band on the wrong side of the road. Where did you get your driving license’ on a punchboard?

4-: From Tot Takes Daddy For Ride, by Phil Willon, published in the Binghamton Press (Binghamton, New York, U.S.A.) of Sunday 28^th October 1951:

MONOLOGUE: In a car.
BY: A father.
ADDRESSED TO: His 3-year-old daughter.
DURING: A Sunday afternoon ride.
[…]
Well, off we go to look at the pretty scenery. . . . Look at that guy cut in . . . I said look at that guy cut in. . . . That man in the big truck, he drove right in front of Daddy. . . . I can’t spank him, dear, but I sure will tell him what I think when we stop for that light . . . HEY, MUTTONHEAD, WHERE DID YOU GET YOUR LICENSE—AT AN AUCTION? YOU OUGHT TO BE DRIVING HARD BARGAINS. . . . There didn’t I tell him?

5-: From The Daily Courier (Connellsville, Pennsylvania, U.S.A.) of Wednesday 21^st November 1951:

In the near future the driver who is asked “where did you get your license, Sears and Roebuck?” will be able to reply: “No, but I bought my car there.” The famous store chain has announced that by Christmas 17 of its units will be offering small models for sale.

6-: From Column 8, published in The Sydney Morning Herald (Sydney, New South Wales, Australia) of Friday 19^th March 1954:

In Parramatta the other day a car driver called out to another:
“Hey, you!” (etc., etc.). “Where did you get your licence?”
Instead of an answer he got a signal to stop.
Four policemen stepped from the car and walked over. “And where’s yours?” one of them asked.
Just to round the story off, the lad who had spoken first hadn’t got one, of course.

7-: From Emotional Makeup Governs Drivers, by Edward M. Wakin, published in The Austin American (Austin, Texas, U.S.A.) of Saturday 23^rd June 1956:

License tests only scratch the surface in finding out whether you should have a license. At one time or another, all of us are tempted to shout at foolish drivers: “Where did you get your license . . . in Woolworth’s?”

8-: From the account of a court case, published in the Victoria Daily Times (Victoria, British Columbia, Canada) of Wednesday 13^th July 1966:

The incident occurred shortly after Mizewich had pulled out of Royal Oak cemetery in front of a truck driven by Logue.
Logue testified he pulled over to the side of the road because he was “shaken” by a near-collision.
Court was told Mizewich pulled his car up behind Logue’s truck and went to the truck window.
Logue said he asked Mizewich “where did you get your licence? In a box of cracker-jack?”

9-: From Aussie Etiket: Or Doing Things the Aussie Way (Sydney: Ure Smith Pty Limited, 1971), by the Australian author John O’Grady (1907-1981):

Because you are driving safely, you will be abused with sentences like ‘Bloody mug, why don’t you buy a bike?’ or ‘Where did you get your bloody licence, Woolworth’s?’

10-: From The New Australia (Sydney: Angus and Robertson, 1971), by the Australian author and journalist Colin Simpson (1908-1983):

A car in front of the taxi stops suddenly, does a U-turn and pulls in at the other kerb. Our taximan leans out of his window: “And where did you ever get a bloody driver’s licence—out of a Weetbix packet?”

11-: From Touchy driver beats pedestrian ‘to a pulp’, published in The Edmonton Journal (Edmonton, Alberta, Canada) of Monday 9^th July 1984:

The man said he was walking along the lane about 11 a.m. when he saw a motorist “driving like a real turkey.” When he asked, “where did you get your driver’s licence from?” the man drove around the block and got out of his car.
The victim said he was then beaten unconscious.

A variant of the phrase is applied to an umpire in the following from Rugby v Rules: An opposite view of Australia’s two major football codes, the description of a game of Australian Rules football by Ken Laws, published in The Sun-Herald (Sydney, New South Wales, Australia) of Sunday 4^th April 1982—in Australian Rules football, the verb shepherd means to prevent opponents from tackling a member of one’s own team by blocking their path:

Early in the piece, the bloke beside me yelled out: “Didn’t you see the shepherd? Where’d you get a ticket, ref, out of a cornflakes packet?”
“Calm down, son,” I said patting him on the shoulder. “They’re allowed to shepherd and he’s not a referee. He’s an umpire.”