So that means it’s saying you just need to unlock the knowledge - just select Treasure Coffer so it’s outlined (like in my original screenshot) and then click on the button marked ‘Unlock’ to unlock it. The 3 in brackets is telling you it wants you to spend 3 knowledge points to unlock it. If you don’t have three knowledge points left over (it’ll tell you just above the three blank boxes you were asking about before) then you won’t be able to unlock it and will need to get more points.
(You said you are level 60, so the only ways to get the points are either eating a Fragment of Power, or drinking a respec potion and resetting all your knowledges).
To place the coffer once you have unlocked the Knowledge, you don’t need any kind of bench you just need to have the materials in your inventory (shaped wood and iron reinforcements). You have to place the Construction Hammer in your character’s hand and open the construction menu as shown in my second screenshot and select the treasure coffer from that menu. Then it will show it ready to placed like any building piece.
1 Like