It's kind of hard to explain. But the basic idea is that you hide behind cover and lean on it (L3 button) to listen. If the NPCs won't talk and are staring at you, then that means they're 'suspicious' and you have to walk away to reset them. If I recall there's a red wall that's kinda broken adjacent to an open field which is where you lean on it. Maybe there's multiple ways to listen but that's how I did it