Specialization classes
Note: Specialization points are obtained at levels 7 and 14.
Mage
Arcane Warrior: In the "Nature of the Beast" quest line, you will find a place in Brecilian Ruins where a spirit is trapped inside something. Set the spirit free and ask it to teach you the specialization.
Blood Mage: In "Arl of Redcliffe" quest line, choose to go into the Fade. Instead of killing the Desire Demon, negotiate with her. When given a reward, choose to learn Blood Magic.
Shapeshifter: Learn from Morrigan (companion) when approval is high enough; or Varathorn (Dalish Camp).
Spirit Healer: Learn from Wynne (companion); or manual from Wanders of Thedas in Denerim (after Landsmeet starts).
Rogue
Assassin: Learn from Zevran (companion) when approval is high enough; or bought from Alarith's Store (Denerim, after Landsmeet starts).
Bard: Learn from Leliana (companion) when approval is high enough; or Alimar (Orzammar).
Duelist: Learn from Isabela (The Pearl in Denerim) if your DEX is high enough to catch her cheating and make her teach you.
Ranger: Learn from Bodann's Wares (Party Camp).
Warrior
Berserker: Learn from Oghren (companion) when approval is high enough; or manual bought from Gorim at Denerim Market.
Champion: Choose to accept reward form Arl Eamon after completing the "Sacred Urn Of Ashes" quest line.
Reaver: Meet with Kolgrim in the Wyrmling Lair just before the mountain top and help him with his task. Pour dragon's blood on the ashes. Note: If Wynne and Leliana are in your party they will join the Guardian in their fight against you.
Templar: Learn from Alistair (companion) when approval is high enough; or Bodahn's Wares (Party Camp).