“A bus station is where a bus stops. A train station is where a train stops. On my desk, I have a work station.” This joke (a work station is where work stops?) has been cited in print since at least 1998. American author William Faulkner (1897-1962) is often credited with the line, but there is no evidence that he ever wrote it.
 
The comedian Steven Wright is famous for his one-liners and has been credited with this “workstation” one-liner since at least 1999.
 
     
The Quote Garden
Job-Related Quotations
If a trainstation is where the train stops, what’s a workstation?  ~Author Unknown
 
Goodreads 
“A bus station is where a bus stops. A train station is where a train stops. On my desk, I have a work station….”
― William Faulkner
       
Google Books
The Edsonian
Edson Family Association, Edson Genealogical Association
Volumes 45-52
1997 (?—ed.)
Pg. XXXVII: 
A BUS STATION IS WHERE A BUS STOPS. A TRAIN STATION IS WHERE A TRAIN STOPS. ON MY DESK, I HAVE A WORK STATION.
   
Google Groups: rec.food.cooking
Elizabeth & Keith Falkner
May 7 1998
A friend in Venice sent this.  He used to be a teacher, which explains a lot:
 
A bus station is where a bus stops.  A train station is where a train
stops.  A work station…
 
Google News Archive
4 July 1998, Gettysburg (PA) Times, pg. A4, col. 3:
A bust station is where a bus stops. A train station is where a train stops. On my desk I have a work station…I guess I’ll stop for this week. — Sherry Correll
 
28 August 1998, Sacramento (CA) Bee, “Move Bugs State Workers,” pg. B1:
“If a bus station is where a bus stops, and a train station is where a train stops, what actually happens at a work station?”
 
22 January 1999, Daily Herald (Chicago, IL), “Feeling low? Log on the Net for a laugh” by Jack Mabley, sec. 1, pg. 14, col. 2:
A bus station is where the bus stops. A train station is where a train stops. My desk is a work station.
 
One Liners, Part III
A bus station is where a bus stops. A train station is where a train stops. On my desk is a workstation…
(...)
Attributed to: Steven Wright
From: Judy BreLea; March 09, 1999
   
5 October 1999, Augusta (GA) Chronicle, Bill Kirby column, pg. 6C, col. 1:
A bus station is where a bus stops. A train station is where a train stops. On my desk, I have a work station.
—Steven Wright
       
Google Books
Enterprise Application Integration
By David S. Linthicum
Boston, MA: Addison-Wesley
2000
Pg. 191:
“If a train station is where the train stops, what’s a workstation . . . ?”—Anonymous
 
Google Books
Getting Started in Chart Patterns
By Thomas N. Bulkowski
Hoboken, NJ: John Wiley
2006
Pg. ?: 
“If a train station is where a train stops, then what’s a work station?”
 
12 October 2006, Taos (NM) News, “Overheard and Unconfirmed,” Tempo Magazine, pg. 50, col. 1:
If a train station is where the train stops, what is a workstation?
 
TechSpot
Quotations on Computers
By bobcat
Sep 22, 2008
(...)
If a trainstation is where the train stops, what’s a workstation…?