The clue to the location of the jade key is on an obscure youtube channel called Radical Random. Radical Random was a favorite of Halliday's as stated on page 56 of most copies.
The Jade Key was the second of the three keys needed in the quest to find Halliday's Easter Egg. It was first mentioned in Anorak’s Invitation. It is inscribed with the following clue to discover the Second Gate:
Continue your quest by taking the test.
On the planet Frobozz in the XYZZY Cluster is a dilapidated white house containing a detailed re-creation of the game Zork, where The Jade Key is located. To earn the Jade Key, the player must collect each of Zork's 19 treasures and place them in the trophy case of the white house. After all of the trophies are collected, the player must blow the Cap'N Crunch Bo'Sun Whistle which was located inside a box of Cap'n Crunch cereal in the white house's kitchen cupboard.
Possession of this key enables an OASIS avatar to unlock the Second Gate.