The Rose of Remembrance is a quest featured in the first Witcher 2 Assassins of Kings Enhanced Edition act.
It is a main-quest activated after you complete Indecent Proposal, or The Kayran: A Matter of Price.
In both cases, you will have to visit the docks and interrogate Ciaran, Iorveths adjutant. The interrogation updates The Assassins of Kings quest, the quest called Returning Memories, and triggers The Rose of Remembrance.
As you talk to Triss, you will receive the first objective of the quest: you must find the rose of remembrance.
“Interrogating Ciaran, made Geralt feel strange. Perhaps it touched a nerve, and it certainly caused anxiety. The Witcher could almost hear the memories locked away in his mind calling for freedom and battering at the door that kept them from him.
Seeing the Witchers behavior, Triss decided there was no time to lose and asked Geralt to find the rose of remembrance. This powerful psychoactive agent could hasten to recover his memory.”
Triss will offer to accompany you for this quest. If you wish you can go alone; however you will miss a romantic scene, which takes place later. If you decide to go alone, and change your mind, she will wait for you at the inn.
Note: It is a good idea to let her join you, because she will lead you straight to the location of the rose.
All you have to do is to follow her south, until you reach the waterfall near the elven ruins.
When you reach the waterfall, talk to Triss and continue to follow her up on the mountain, where you will find the roses. Take one and give it to Triss (you will see the consequence of this action later).
During the next cutscene some thieves will appear. Get ready to fight them and watch the cutscene showing you and Triss falling into a secret chamber under the mountain.
First, loot the chest in the bathroom, then talk to Triss and tell her that she could use a bath, to trigger the cutscene mentioned earlier.
After your conversation with Triss, Roche will appear telling you that it is time to go back to Flotsam. The Assassins of Kings quest updates again, and you should focus on it in order to advance in the game.
The Returning Memories quest also updates.
Note: At this point is a good idea to complete all side-quests that appear in your Journal, except for the Mystic River and Melitele’s Heart which require some items you will find later in the game.
To continue the series of main quests, you must advance The Assassins of Kings quest, which will activate the next quest in line, named Where is Triss Merigold?