After travelling to, or finding the Wayshrine of Learning (activated by Prelate Celegriath), head towards the northernmost tip of the (unfrozen) lake. On one side of the lake you should see a steep path that will take you up and over a hill towards the next Wayshrine. Opposite this path, on the other side of the unfrozen lake, will be a clearing. The Giant that roams it holds the Amethyst Paragon.