wondering vs questioning

wondering is not a noun while questioning is a noun.

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

As adjectives, wondering and questioning are synonyms defined as:

Other synonyms of wondering include inquisitive, speculative.

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

wondering (adjective)	questioning (adjective)
showing curiosity	showing curiosity
	marked by or given to doubt
	perplexed (as if being expected to know something that you do not know)