At the beginning of the chapter, wait for Nadine and Sam to finish talking. They’ll both stand at the edge of the cliff, and you can wander over to Sam for the conversation prompt to appear over his head.
Press triangle for conversation #14.
After falling from the waterfall and swinging over to the cliffs, you’ll come to a yellow fence with a gap in the top.
Nadine will have followed you, so wait for her to catch up for conversation #15.
Afterward, when you’ve helped Sam cross the broken bridge, stick close to him for conversation #16.
Not long after this, you’ll have to rope swing to some rocky slopes and then climb up into a cave opening to activate a cutscene.
Once you’ve taken out the Shoreline mercenaries, follow Nadine to the caved in exit for conversation #17 – the last optional conversation of the game!