“What do elves do after school?”/“Gnomework.”

A Christmas riddle is:
 
Q: What do elves do after school?
A: Gnomework.
 
The riddle has been cited in print since at least 1984.
 
             
Google Books
The Zaniest Riddle Book in the World
By Joseph Rosenbloom
Illustrations by Sanford Hoffman
New York, NY: Sterling Publishing Company, Inc.
1984
Pg. 93:
What does an elf do when it gets home from school?
Gnomework.
 
24 July 1988, Newsday (Long Island, NY), “Smiles,” Kidsday sec., pg. 1:
What does an elf do after school?
Gnome work.
Tom Stewart, Farmingdale
   
Google Books
December 2001, Boys’ Life, “Think & Grin,” pg. 62, col. 2:
Ken: What does an elf do after school?
Jen: What?
Ken: Gnomework. — Michael Peters, Uniontown, Pa.
 
25 September 2002, Los Angeles (CA) Times, “The Kids’ Reading Room; Jokes & Riddles,” pg. E7:
What does an elf do when it gets home from school? Its gnomework. (Nancy, 7, Eucalyptus Elementary, Hawthorne)
 
Twitter
Manzoor Abdul Majeed‏
@manzoor1984
What do elves do after school?
Gnomework!
6:41 AM - 14 Jun 2009
 
Twitter
Walt‏
@WaltCade
What did the little elves have to do when they got home from school? Gnome-work!
7:43 AM - 25 Dec 2016
 
Google Books
Katie Woo’s Hilarious Holiday Jokes
By Fran Manushkin
North Mankato, MN: Picture Window Books, an imprint of Capstone Press
2017
Pg. 27:
What do the elves do after school?
Their GNOME-work.
 
Google Books
101 Christmas Jokes
By Jack Jokes
PeteyRF Creative
2017
Pg. ?:
What did the little elves have to do when they got home from school?
Gnome work!