When you enter the room with Oka's chest, there are some yellow banners that appear on the back wall. They have symbols (something like a skull, snake, etc.). You have to light up the obelisks in that room with the symbols that are showing on the yellow banners. Then Oka's chest will appear.
If the banners disappear / fade away before you get to see what is on them, just leave the room and come back in again, and the yellow banners will re-appear.
i am on the quest oka's chest but i can't find the chest?
If I rememeber correctly, you get the obelisk code when you first walk in. Go through the entrance like normal. Once inside - DO NOT MOVE. Just look ahead - along back wall. There will be 3(?) tablets that reveal the codes to light the obelisks in order. If you take a step forward, the tablets will disappear.
Once you light the obelisks, the chest will appear towards the entrance/exit.