Winged Reaver is a DLC quest available in Dragon's Dogma.
Note: "Griffon" is misspelled in the in-game quest objectives, contrary to other in-game spellings of the word "Griffin".
"A griffin has been spotted near Hillfigure Knoll. To allow it to roam free now is to sow the seeds of misfortune for the times to come."
This quest is available on the notice board at Pablos' Inn in Cassardis after meeting the Duke in the quest Come to Court.
Like many other quests, it is not nececssary to specifically slay the Griffin
at Hillfigure Knoll
. Any slain Griffin will complete this quest.
Completing the main story quest Griffin's Bane will simultaneously complete this quest.
As for the griffin the quest mentions, there are chances to encounter it flying nearby the camp and the broken sarcophagi just to west of Hillfigure Knoll.
Griffin Strategy Vol. 2 states that taunts or a carcass can be used to lure a griffin. Shield Drum, as a taunt, is more effective than a carcass to attract the Griffin.