What happens if my opponent failed a Confusion check last turn and I try to use Sudowoodo's "Watch and Learn" attack? Would Sudowoodo take 3 damage counters?
If the Pokemon failed its attack because of Confused, an attack was not used. Sudowoodo's Watch and Learn would simply do nothing.
Source: TPCi Rules Team (2018-03-01)

Relevant cards

Note: All applicable cards may not be listed below.
XY9_67