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