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