Start a Combat challenge on the 4th map - Ice Queen.
Pick the 3rd character who has Klonk available (Press Y before picking a character to see their inventory and what icon is associated, so you know how to equip klonk)
Press B until you have klonk selected and roll your way to the right where you meet the target and several other enemies. Throw the Klonk and hope for the best! May take a few tries, (hopefully) here is a video of me getting the achievement: