If I attack with Golurk V's "Rewind Beam" and do enough damage to KO my opponent's evolved Pokemon that has the Vengeful Punch tool attached, does Golurk V take 4 damage counters?
No. Rewind Beam devolves the Defending Pokemon, and when its earlier stage is Knocked Out that is no longer the Pokemon that had taken damage from the attack.
Source: TPCi Rules Team (2023-11-09)