To receive the instance quests for Treasure Trove in Ravenfell you need to be lvl 48. The prequests can be done at lvl 46/47.
Here are the quests you need to do to open up the instance:
The Nameless Port's History (NPC Kimoran) Inspect the Nameless Port (NPC Ubame) Organize Peace (NPC Ubame) Tarnished Silver Necklace (NPC Degun) Last Wish (NPC Ubame) The Cost of Honor (NPC Yaniha Bimey, Marlow Rhodes) Suspicion (NPC Afellow) Mysterious Scroll (NPC Kolodo) Pirates' Developing Agent (NPC Cheney Chanep) Written in Blood (NPC Cheney Chanep) Truth? (NPC Skikude) Copy (NPC Shikude) Legacy of Inheritance (NPC Kolodo) Pirate Appraiser (NPC Kolodo) Non-existent Clues (NPC Shikude)
NPC Kain (on the ship) Ravenfell's Living History Dirty Decryption Book Good Drinks Are Just The Start Big Lobster In The Sand Dunes Truth Telling Liquor Complimentary Guard Truth on a Sheepskin Parchment A Faithful Servant
* Updated this list of prequests since the old version was missing some prequests (back in the day you had to do the other quests before reaching level 47 to actually get the level as Coast of Opportunity and Xaviera did not exist, thanks for the reminder Uure (in case you read this))