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