Spesically What you need to do is this:
After the dispute scene with the templar guy and the chantry priestess in Val Ryoux Cassandra will go "AH! A arrow on the ground with a note on it. where did it come from?" Search it. you'll get a message and a quest keyed up. you will get two quest marks around where you are at. One is at the docks and there's one at a eatry area with a musician.
At the docks hit the "SEARCH" button. you should get an arrow pointing to a "redish smudge" on the ground near some boxes. When it gets confirmed to be serached search it to get the note.
At the eatry hit the "SEARCH" button. you should get an arrow pointing to a "redish smudge" on the ground around some people eating. When it gets confirmed to be serached search it to get the note.
Go to your map and clock on the "Quick travel" marker spot and quick travel to floor 2 and roughly the one next to the bottom left hand one. After the loading is done search around the quest zone and hit the "SEARCH" button. you should get an arrow pointing to a "redish smudge" on the ground which should be preaty visible. When it gets confirmed to be serached search it to get the note.
Once all three notes are gathered you should get a confirmation message for your Journal section that were in "The Inner Circle" you would need to "Go to your world map and travel to the 'marked location' on the world map".
Go to your world map and there should be a circle cross like icon on the world map close to Val Ryoux where if I remember right you get a mission name with a picture of Sera. Click on it and do the mission. It's very self explanatory from here.