sceptical vs questioning

sceptical is not a noun while questioning is a noun.

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

As adjectives, sceptical and questioning are synonyms defined as:

Other synonyms of sceptical include doubting, skeptical.

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

sceptical (adjective)	questioning (adjective)
marked by or given to doubt	showing curiosity
denying or questioning the tenets of especially a religion	marked by or given to doubt
	perplexed (as if being expected to know something that you do not know)