**Contains Spoilers** but you knew that already...
These are the only RB events needed to unlock the achievement presented in order. I just now unlocked the achievement as I am typing this. Also, thank you [Animosity] who pointed out that you don't have to hold RB throughout the entire sequence, as long as it's pressed or tapped during each one it will work. Additionally [Chosen One 41] confirms that it can't be unlocked by re-watching them in the demo viewer :
 When you arrive at Krasnogorje Mountaintop to meet Eva, there will be a cutscene. Towards the end of when The Boss is leaving, hold RB.
 In the Groznyj Grad Torture Room cutscene, near the end when Ocelot walks away, hold RB.
 After the Shagohod Fight at Groznyj Grad Runway Bridge, right after Volgin is set on fire, hold RB.
 After fighting 'The Boss' and putting a bullet in her head in the cutscene, her horse will appear, hold RB.
During the game's ending:
 During the cutscene at the when the President shakes Snake's hand, hold RB. You'll see Ocelot in the window if you look left while holding RB.
 Finally while at the graveyard when Snake salutes, hold RB.