List of Trainer levels

Each Level requires a certain amount of Experience Points and for achieving each level Trainer is rewarded with certain items.

Level-up Researches
Leveling-up past level 40 requires XP and new Level-Up Researches. This mechanic was announced in the update GO Beyond.

Power up a legendary Pokemon 20 times Win 30 raids Catch 200 Pokemon in a single day
 * Level 41:
 * Level 42: Evolve Eevee into each of its available Evolutions. Use certain Evolution items on specific Pokémon.
 * Level 43: Research involving Gym battles and Raid Battles. A certain number of Platinum medals is required.
 * Level 44: Battling other Trainers relate research.
 * Level 45: Team GO Rocket related tasks.
 * Level 46: Complete 100 Field Research tasks, hatch 30 Eggs, and use GO Snapshot 7 days in a row.
 * Level 47: Win raids with teams that meet certain qualifications.
 * Level 48: Friendship with your Buddy Pokémon. From kilometers walked to the number of Souvenirs collected.
 * Level 49: Friendships with other Trainers: Send Gifts, acquiring Lucky Pokémon through trades, and more.
 * Level 50: Make Excellent Throws, catch Legendary Pokémon, and defeat Team GO Rocket Leaders with Pokémon under 1,500 CP