What all goes in my Trainer Passport?

Solution 1:

According to Serebii.net, the 15 pages are:

Official Pokémon Trainer: You took the first step as a Pokémon Trainer!
Melemele Trial Completion: Complete the Melemele Island Trial
Akala Trial Completion: Complete the Akala Island Trial
Ula’ula Trial Completion: Complete the Ula'ula Island Trial
Poni Trial Completion: Complete the Poni Island Trial
Island Challenge Completion: With this stamp, all Pokémon will obey your every command.
Melemele Pokédex Completion: You registered all Pokémon on Melemele Island!
Akala Pokédex Completion: You registered all Pokémon on Akala Island!
Ula’ula Pokédex Completion: You registered all Pokémon on Ula’ula Island!
Poni Pokédex Completion: You registered all Pokémon on Poni Island!
Alola Pokédex Completion: You registered all Pokémon in the Alola region!
50 Consecutive Single Battle Wins: You achieved 50 consecutive wins in Single Battles at the Battle Tree.
50 Consecutive Double Battle Wins: You achieved 50 consecutive wins in Double Battles at the Battle Tree.
Poké Finder Pro: You obtained the final version of the Poké Finder!
50 Consecutive Multi Battle Wins: You achieved 50 consecutive wins in Multi Battles at the Battle Tree.

Hopefully that explains your question