“Ghost Knight of Jackal”’s effect activates when you send a monster to the Graveyard.
If your “Ghost Knight of Jackal” attacks a face-down “Jowls of Dark Demise”, your opponent takes control of “Ghost Knight of Jackal” at the time that “Jowls of Dark Demise” is sent to the Graveyard, and “Ghost Knight of Jackal”’s effect disappears.
If “Ghost Knight of Jackal” is removed from the field or flipped face-down before the monster it destroyed is sent to the Graveyard, then “Ghost Knight of Jackal”’s effect is not applied.
If “Final Attack Orders” is active, you can Special Summon a monster destroyed by “Ghost Knight of Jackal” in Defense Position, but it is changed to Attack Position immediately.
If your “Ghost Knight of Jackal” destroys a monster you own that is on your opponent’s side of the field, the effect of “Ghost Knight of Jackal” is not applied because it only applies to “an opponent’s monster” that is destroyed.
If “Ghost Knight of Jackal” attacks “Ghost Knight of Jackal”, neither effect is applied.