Did you return to the main game and try to learn something there? You can learn from Edmond, the poisoned imp after you jump down the pit in the arena, the imp Tax (until you play his game and he leaves) and various NPCs once you reach the citadel.
Have you checked your skill selection after reading a spell book? If so, do the skills listed in the book become available? Fergus drops a spell book, as does the thirsty prisoner after he is given a specific bottle of water, and there is another to be found shortly after jumping down the pit.
