Here is the full list of all 57 Psychonauts 2 achievements. It takes around 25-30 hours to unlock all of the achievements on Windows.
Acquire all Upgrades
Find all Figments
Achieve Rank 100
Return to where it all started
Tag all Emotional Baggage
Purchase all Pins
Max out your PSI Pop capacity
Max out your Dream Fluff capacity
Purchase all Otto Shot Filters
Completely fill your Astral Wallet
Crack all Vaults
Scavenge all MISSION CRITICAL PSYCHONAUTS ASSETS
Dissolve the Deluge of Grulovia
Recover your mental energy with a Dream Fluff
Frequent Fatherland Follies
Break all 3 Gramaphones in Fatherland Follies
Soothe Lucrecia's Lament
Throw a Regret's anvil at another enemy
Peruse Cassie's Collection
Empty Bob's Bottles
Discover the Astralathe
Raid the Tomb of the Sharkophagus
Repair Ford Fractured
Treat Ford's Follicles
Complete Gisu's Psychoseismometer Quest
Equip 3 Pins at once
Complete Queepie Quest
Throw a Judge's gavel back at him
Achieve Rank 50
Bowl Strike City
Plate Compton's Cookoff
Pyro 3 enemies at once
Deliver Cruller's Correspondence
Complete PSI King's Sensorium
Fully upgrade a Badge
Find the real Panic Attack during his Phantom attack
Upgrade to the Astral Wallet
Complete Lili's Request
Help Dion Setup Aquatodome
Find the Family Camp
Tune in to a Stray Thought
Take a photo with the Otto Shot
Talk to Milla in her Office
Revisit a brain through the Collective Unconscious
Visit the Collective Unconscious
Cool Hollis' Hot Streak
Shut Down the Luctopus
Make a connection in Hollis' Classroom
Achieve Rank 10
Upgrade your first Badge
Receive your first assignment
Equip your first Pin
Combine PSI Cards with a PSI Core at the Otto-Matic
Achieve Rank 2
Navigate Loboto's Labyrinth
Consume a PSI Pop to restore some mental energy
TK throw an object to stun an enemy