If I have Celesteela GX with "Force Canceler" Ability active, what happens if my opponent uses Venomoth GX's "Ten-Card Return GX" attack?
The damage portion gets blocked, but your opponent still gets to shuffle their hand into their deck and draw 10 cards because that part is not being done to YOUR Pokemon.
Source: Unbroken Bonds FAQ (2019-04-19), TPCi Rules Team (2019-05-09)

Relevant cards

Note: All applicable cards may not be listed below.
SM10_12
SM10_12
SM10_163
SM10_163
SM10_193
SM10_193
SM10_208
SM10_208
SM10_216
SM10_216
SM10_228
SM10_228