Find the Legacy of the Aspects and return it to Braug Dimspirit near the entrance to Talondeep Path in Stonetalon Mountains.
You have passed Dorn's tests, and now you seek to pass your next trial. Very good. But up until now, your challenges have been childish. It is easy to test your body--your mind is another matter completely.
I shall explain it simply: find the book I name, study it, and answer my question about its contents.
What book, you must be asking? The Legacy of the Aspects. It can be found at the bottom of Dor'danil in southern Ashenvale, protected by the dead druids and their slayers.