This The Last of Us 2 New Game Plus Guide explains everything you need to know about what you unlock after beating The Last of Us 2.
What Is New Game Plus Mode in The Last of Us Part 2?
New Game Plus Mode in The Last of Us Part 2 allows you to play the game again, maintaining all your upgrades and weapons from your first playthrough. You will need to play at least some of New Game Plus to fully upgrade your character if you want to get the platinum, i.e all 26 trophies.
No new gameplay elements, skills, weapons, or enemies are introduced in this mode.
Source: IGN.com The Last of Us 2 New Game Plus Guide