How to help Triss finish what she has to do in Novigrad?

To fix these issues you can use the console.

If you are stuck at the "Brothers In Arms" quest with Triss, open console and type in the following "below" in this order. It will start a quest that is missing from your game. The quest to find Philippa Eilhart "Redania's Most Wanted". After you complete that quest and turn it in to Radovid, it will trigger "Now or Never, and so on. You game is back on track and fixed.

addfact(q302_completed)
addfact(q302_post_mafia_completed)
addfact(sq302_start)

Reason the quest gets bugged. After you find Whoreson and complete the quest, you must leave the area through the gate. If you do not, it will not trigger the mission "Redania's Most Wanted" and so on.

There is a mod that lets people fast travel from anywhere and this is what causes the issue for most people. They fast travel out of Whoresons house instead of passing through the gate which of course a ruins a huge chunk of the game.

The questline broke to using the Fast travel everywhere mod.

Apparently, this is because I used the Fast Travel From Anywhere mod during the Get Junior quest.

I figure this might be beneficial to others, so I've made a small list of quests that will break if you fast-travel out of a building during these quests:

Novigrad - Pyres of Novigrad: Do not fast travel out of Triss's house. You won't be able to talk to the beggars or follow the thief.

Novigrad - Get Junior: Do not fast travel out of Junior's mansion. This prevents you from completing a main quest and several 2ndary quests including "A Favor for Radovid", "Redania's Most Wanted", "Now or Never".

Kaer Morhen - To Bait a Forktail:
After killing the forktail, you need to race Eskel down the mountain. If you fast travel out of the cave, you'll need to go back to meet Eskel.

Basically, the rule of thumb is to avoid using the instant fast travel while you're on a mission or in a mission area.

I can confirm that this was the issue as on a 2nd replay I refrained from using fast travel mod in quests, and everything worked as expected.

Source: www.reddit.com