quizzical vs questioning

quizzical is not a noun while questioning is a noun.

Word	Noun	Adjective	Verb	Adverb
quizzical	No	Yes	No	No
questioning	Yes	Yes	No	No

As adjectives, quizzical and questioning are synonyms defined as:

quizzical and questioning: perplexed (as if being expected to know something that you do not know)

quizzical (noun)	questioning (noun)
	a request for information

quizzical (adjective)	questioning (adjective)
perplexed (as if being expected to know something that you do not know)	showing curiosity
playfully vexing (especially by ridicule)	marked by or given to doubt
	perplexed (as if being expected to know something that you do not know)