Missing Persons - Skellige
This quest is given to you after completing Echoes of the Past, a Skellige Story Quest. All you have to do for this quest is follow Yennefer and go through the dialogue. It's a very short quest and it starts/ends in the same village after talking to only a few people.
Upon completion of this quest you'll automatically be given the Story Quest Nameless and thrown into it. After Nameless there will be another quest that you're thrown into by the name of The Calm Before The Storm. Keep this in mind if you're planning on starting this quest chain now.