Speak to Lorokeem in Shattrath's Lower City. *WARNING!* You can only select one alchemy specialization.
My knowledge of alchemy is vast. It is, however, general in nature. If you wish to specialize, you will have to find others who have narrower fields of study.
If you wish to specialize in elixir creation, I would recommend that you seek the help of the arakkoa known as Lorokeem.
His knowledge of elixirs is unmatched, yet he squanders his skill pursuing an elixir of eternal life. Find him and see what he can teach you.