What is the rear hub of a Giant ATX 2 2019/2020?
Freewheel have almost completely been superseded by freehubs and cassettes, however the Giant ATX is an inexpensive bike with a Tourney level groupset, so It could conceivably have a freewheel.

It's simple to look up the bike's specs and find out. This is the ATX 2 page at the giant site. The site says it has a Shimano MF-TZ500 14x34 'cassette'. The 14 tooth small sprocket gives us a clue that this is a freewheel. 

Looking at the Shimano page for the MF-TZ500 we see that it is indeed a 7 speed freewheel.