This absolutely fabulous image was probably created in the mid-1940s.  Knerr drew essentially this same image more than once.  This one was reproduced on the cover of a little reprint book, "The Katzenjammer Kids," published in 1986 by Blackthorne Publishing.  It is not clear whether the color you see here was in the original or only in the printed version.  I do know that a hand-colored original of a similar illustration has survived and is held in a private collection.