Use the Divination Scryer in the heart of the Great Ossuary's basement in the Scholomance.  Doing so will bring forth the spirits you must judge.  Defeating these spirits will summon forth Death Knight Darkreaver.  Defeat him and reclaim the lost soul of the fallen charger.$B$BGive the Charger's Redeemed Soul and the Blessed Enchanted Barding to Darkreaver's Fallen Charger.