Ok
If you are stuck in the Cave of Wonders this is likely your problem:
Examine the pillar blocking the exit of the Treasure Room. It'll say something about exploring the ruins beneath the cave. Do just that. First, go to the Hall area and drop down into the bottomless pit anywhere ya'd like. I'm pretty sure you'll land in the Dark Chamber. If not, sorry. Anyway, I don't know exactly where to exit the Dark Chamber. You now need to go to the Silent Chamber. It'll be a chamber with only one strip of land. One the right side of the land will be a wall, and on the left side will be stairs leadig up into the upper level of the cave. There will also be a Blue Trinity mark on the spiece of land, too.
Hop on the land, and then drop off into the water on the other side of it. There will be a "hidden" door in this area. Go through it, to find yourself iin the Hidden Chamber. Hop on the piece of land, and target the pillar across the water. You can either jump towards it and hit it with your Keyblade, or just use a fire spell on it. Doing so wull cause it to fall a little, and trigger a short cut scene. Now navigate your way back to the Treasure Room. As you will see, the pillar is gone from blocking the doorway. Enter the door to fight Jafar.
Hope that helped. I know it wasn't too clear! pm me if you need any more help with Kingdom Hearts!