Golden egg is a unique item in the Blood and Wine expansion. One must seek out Syanna during The Night of Long Fangs and then enter the Land of a Thousand Fables. After talking to Joss, go pick up the contract off the notice board in the small town to the right (past the fields).
Put the egg in your consumables slot and eat the egg; it will give you one free skill point when you do so. Important: You must consume it before you leave the fabled world or else it disappears from your inventory (as it is part of the illusion).
- Though its type is set to be "other", it appears in "Food and drink" section of the inventory.