Rocky Helmet punishes incoming attacks by placing 2 damage counters on the attacker whenever the holder, while Active, is damaged by an opponent's attack, even if the holder is knocked out. The Vivid Voltage wording rephrased the location language from Active Pokémon to the Active Spot but kept the same effect.
Rocky Helmet debuted in the Black and White era's Noble Victories, then reprinted in Boundaries Crossed with both a standard Uncommon and a Secret Rare version, all illustrated by Ryo Ueda. It returned in the Sword and Shield era's Vivid Voltage with new art by Studio Bora Inc., and again in the Scarlet and Violet base set with art by Ayaka Yoshida. Our catalog lists 5 printings.
Rocky Helmet is based on a held item first seen in Pokémon Black and White, which hurts any attacker that touches the Pokémon holding it.
The Noble Victories printing is Rocky Helmet's first release
The Boundaries Crossed Secret Rare printing pairs the original wording with a rarer treatment
The Vivid Voltage printing introduced the Active Spot wording
Yes, the effect still applies even if the holder is knocked out by the attack.
It replaced the Active Pokémon phrasing with Active Spot and refers to an attack from your opponent's Pokémon, without changing the effect.
From Noble Victories (2011) · 3 printings
If the Pokémon this card is attached to is your Active Pokémon and is damaged by an opponent’s attack (even if that Pokémon is Knocked Out), put 2 damage counters on the Attacking Pokémon.
From Vivid Voltage (2020) · 2 printings
If the Pokémon this card is attached to is in the Active Spot and is damaged by an attack from your opponent's Pokémon (even if it is Knocked Out), put 2 damage counters on the Attacking Pokémon.

Rocky Helmet
Pokémon Tool
First printed in Noble Victories (2011)
If the Pokémon this card is attached to is in the Active Spot and is damaged by an attack from your opponent's Pokémon (even if it is Knocked Out), put 2 damage counters on the Attacking Pokémon.