The following chapter of our guide to Assassin's Creed Odyssey contains a list of all the Ainigmata Ostraka available on the Kephallonia Islands, along with their solutions. There are three Ostakons in the starting location: Bottomless Lake, Ash to Ash, Fatal Affection.
Ash to Ash
The location of the Ainigmata Ostraka: Marcos' Vineyard. The item can be found atop the building shown in the picture above.
Solving the puzzle: Kausos Village. Enter the shrine and search the place to solve the puzzle.
The location of the Ainigmata Ostraka: Melissani Cave. Jump down, dive and find the items at the corpse.
Solving the puzzle: Go to the Koliadai Coast and then to the lake in the south. Dive and swim downwards. You will reach a statue underwater - swim towards it and interact with the statue to solve the puzzle.
The location of the Ainigmata Ostraka: Odysseus Palace, Ithaka the item can be found in one of the buildings - if you will have any trouble finding it, you can resort to the short clip we've included. See above.
Solving the puzzle: Go to the north of the Odysseus Palace. In order to solve the riddle, go to the goat farm and search the corpse of one of the animals.