I'm pretty sure that GP's Q is an ability that applies on-hit effects?
quick checks
Wiki info:
"Parrrley is a single targeted ability.
Applies on-hit effects, on-attack effects, life steal and fully critically strike.
Parrrley behaves like a melee auto-attack.
Parrrley can be affected by on-being hit effects coming from champions and items.
Frozen Mallet item.png Frozen Mallet and Iceborn Gauntlet item.png Iceborn Gauntlet will apply the strongest melee version of their slows.
Phage item.png Phage and Trinity Force item.png Trinity Force will trigger the strongest melee version of the movement speed bonus.
Tiamat item.png Tiamat's and Ravenous Hydra item.png Ravenous Hydra's splash damage will trigger, and Parrrley will not interact in any way with Runaan's Hurricane item.png Runaan's Hurricane's passive.
Parrrley can be Aegis Protection.png blocked, Counter Strike.png dodged or Riposte.png parried.
Banshee's Veil item.png Spell shields will block the ability.
This ability is considered to be a projectile for Unbreakable.png Unbreakable and Wind Wall.png Wind Wall.
Additional Information:
Parrrley resets Gangplank's autoattack timer.
Every unit killed by Tiamat item.png Tiamat's or Ravenous Hydra item.png Ravenous Hydra's splash damage or the procs from Statikk Shiv item.png Statikk Shiv and Iceborn Gauntlet item.png Iceborn Gauntlet will grant Parrrley's bonus gold and refund mana.
This makes it possible to refund more mana than the ability costs (returning the full mana used with 2 kills and returning more than the used mana with 3+ kills)."
It says it's an ability, so AFAIK it should apply the echo.