If you are in the village, go backwards and continue until you reach an area where there is an path that winds down a ledge. On the side, there will be a door where you need to input a code. There are various areas around the island where you can find numbers that go into the code. You don't have to worry about memorizing them because they will be there when you go back to the door. When you have all four, go input the code in the door, and Wakka will be waiting for you inside.
in kevins house
once you get into the cave, he's pretty close to the entrance, sitting up against a wall. getting near him SHOULD trigger a cutscene, afterwhich you get to explore the cave, and....i think you get the white mage sphere from that area.
they are randomly generated for each game. you can find the codes in besaid and you first have to examine them.
There is a cave south of Figaro mixed in with the mountains
You get it after you beat Hecatoncheir in the Cave of Shadows.
Cave in the underworld at in the western part of the map
An enemy found at Mysidia Cave and Tropical Island. A Fairly weak foe able to inflict abnormal status, but is resistant to physical attacks.
ice magic works great
You have to get through the Sochen Cave Palce to get to Old Archades and then it will explain itself
The Dwarf Cave can be reached by sailing to the north west corner of the Aldi Sea. Land at the port there and then walk south to find the cave entrance.
The Skeleton Key is actually not an item as you would expect but a button of sorts. In the Sealed Cave of Final Fantasy III there's a dead end with skulls. One of these skulls is the actual key you need to interact with to proceed.
Edward gives it to you when you visit him in Troia castle, before you go to the Magnetic Cave.