who knows what
see under what have you.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
Examples from the Web for who knows what
Like mushrooms, in a single sight we spring up—a pen in our hands, very little in our brains, and who-knows-what in our hearts!The Complete Essays of John Galsworthy
The little model gave him a look with who-knows-what of reproach in it, and, faithful to her training, went submissively away.Fraternity