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