Read from the World of Warcraft client build files.
How Nightsfall Shoulderplates Compares
Who It Suits
Plate is the armor type Death Knight, Paladin and Warrior wear. With Strength or Intellect, Nightsfall Shoulderplates suits Arms, Fury and Protection Warrior; Holy, Protection and Retribution Paladin; Blood, Frost and Unholy Death Knight.
Transmog Sets
Nightsfall Shoulderplates is part of the transmog set Leyline Defender's Sunplate Armor (Warrior, Paladin and Death Knight only). The other 16 pieces:
Blizzard numbers items as they are created, so the named items next to ID 139060 (139055 to 139065) were usually added in the same batch as Nightsfall Shoulderplates: the same quest line, zone, vendor or reward set.