line of inquiry vs line of questioning

line of inquiry and line of questioning both are nouns.

Word	Noun	Adjective	Verb	Adverb
line of inquiry	Yes	No	No	No
line of questioning	Yes	No	No	No

As nouns, line of inquiry and line of questioning are synonyms defined as:

line of inquiry and line of questioning: an ordering of questions so as to develop a particular argument

line of inquiry (noun)	line of questioning (noun)
an ordering of questions so as to develop a particular argument	an ordering of questions so as to develop a particular argument