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