When another monster with "Jackknife" in its card name is called on top of this card, this card will be put into the soul of that monster.
When another monster with "Jackknife" in its card name is called from the deck with this card's Act ability, the Call Cost of that monster does not have to be paid.
In response to the activation of this card's Act ability, if this card is removed from the field with a Counter such as Magical Goodbye, you may still pay 2 gauge and search your deck for a "Jackknife" monster when the Act ability resolves, but that monster will be unable to enter the field, as it cannot be placed over Jackknife Dragon anymore. That monster will have to be shuffled back into the deck instead. However, since paying 2 gauge during the resolution of this ability is optional, it's possible to simply choose not to pay it, and let the rest of the ability fail to resolve.
When another monster with "Jackknife" in its card name is being called on top of this card from the hand, if the opponent casts Begone!! as a Counter to nullify the call, the Jackknife monster will be sent to the drop zone without entering the field, along with the Jackknife Dragon that was already put into its soul as part of its Call Cost.