Here is the full list of all 39 Return to Monkey Island achievements. It takes around 15-20 hours to unlock all of the achievements on Windows.
Answered One Hundred Trivia Questions Correctly
Reached The End In 2 Hours Or Less
Answered Seventy-Five Trivia Questions Correctly
Rescued Wally From Monkey Island
Explored The Entire Ocean Floor
Performed The Ole Switcheroo With The Replica Flag
Died For Real
Got Hired With All Four Mop Heads
Attempted To Steal The Cook’s Mop
Offered To Donate To The Earthquake Relief
Found Cogg Island
Ahoy! More Than Twenty Times
Did Gullet A Favor
Found All The Copies of ‘At The End Of The Plank’
Answered Fifty Trivia Questions Correctly
Got To The Heart Of The Problem
Braved The Scorched Alaska
Listed Every Mess On The First Swab’s Report
Answered Twenty-Five Trivia Questions Correctly
Fulfilled Your Restroom Obligations
Returned To The World You Know
Started Part Five
Gave Stan His Toothbrush
Told Everyone On Mêlée Island That You Are Looking For The Secret
Became A Prize Chum
Waited Patiently To See Carla
Collected More Than Twenty Trivia Cards
Let The Lumpsucker Escape
Thoroughly Examined All Of Wally’s Stock
Decked Out The Sea Monkey II With Spooky Skulls
Started Part Four
Started Part Three
Answered Ten Trivia Questions Correctly
Swabbed The Hold Twenty Times
Started Part Two
Freed Otis
Convinced Cobb To Tell You About LOOM
Started Part One
Shared Your Luck