You must complete a large portion of Grizzleheim and Wintertusk before you can obtain your Mana Burn spell.
You are currently working on the Grizzleheim quest "Metal Health" given to you by Einar Thunderhammer in Savarstaad Pass. Complete that, and continue with the main quests in Grizzleheim and Wintertusk.
Doing so will also open up another spell quest that you missed at level 55. See this wiki entry for information on the quest for Mana Burn http://www.wizard101central.com/wiki/Quest:No_Pain,_No_Agravaine and use the prequest links to see what you need to be given that quest.
