If my Jumpluff with the "Fluffy Barrage" Ability attacks and KO's my opponent's Active Pokemon, do I get to attack again if my opponent promotes a Galarian Weezing with "Neutralizing Gas" Ability before the second attack?
No, because Neutralizing Gas disables Fluffy Barrage before Jumpluff can attack a second time.
Source: TPCi Rules Team (2022-03-03)

Relevant cards

Note: All applicable cards may not be listed below.
SWSH7_4
SWSH7_4
SWSH2_113
SWSH2_113