Knowledge Vault is a rare Artifact card from Legends (LEG), collector number 281. Current market price: $41.77, TCGplayer market prices via Scryfall.
{2}, {T}: Exile the top card of your library face down. {0}: Sacrifice this artifact. If you do, discard your hand, then put all cards exiled with this artifact into their owner's hand. When this artifact leaves the battlefield, put all cards exiled with it into their owner's graveyard.