Bring a mysterious artefact to your sorceress friend to learn more about it.
The Witcher 3: The Soldier Statuette
This quest is very similar to The Nobleman Statuette. Both need to be attempted before Triss Merigold leaves Novigrad as a result of Now or Never, if you do not successfully romance her.
The mission is triggered when the Jade Figurine quest item is obtained during A Dangerous Game, from the secret room on the top floor of Caesar's house.
Bring the statuette to Triss in her lodgings or at the Rosemary and Thyme. She escorts you to The Bits and casts a spell, revealing a very confused Nilfgaardian soldier. Send him on his way to complete the quest.