whatnot vs knickknack

whatnot and knickknack both are nouns.

Word	Noun	Adjective	Verb	Adverb
whatnot	Yes	No	No	No
knickknack	Yes	No	No	No

As nouns, whatnot and knickknack are synonyms defined as:

Other synonyms of whatnot include bric-a-brac, knickknackery, nicknack.

whatnot (noun)	knickknack (noun)
miscellaneous curios	miscellaneous curios
	a small inexpensive mass-produced article