We read that Christ, when he was at Jerusalem, was wont at night for privacy to retire to the mount of Olives, Luke 21:37, Luke 22:39 and it should seem that he was wont ordinarily to go to this garden, which made Judas know the particular place where he might find him.
Related Commentaries of John 18:2
John 18:2
2 And Judas also, which betrayed him, knew the place: for Jesus ofttimes resorted thither with his disciples.