It's impossible to know everything that is happening in Anchorage, knowing where to look helps.
Visit Anchorage: https://www.anchorage.net/events
Anchorage Press: http://www.anchoragepress.com/calendar/#/
Major Annual Events
Fur Rendezvous: A annual celebration of the early fur trading traditions, starting late February.
Alaska State Fair: The Alaskan State Fair is the most well attended Fair in the country, compared to a state's population. Takes place in late August to early September in Palmer.
Alaska Federation of Natives Convention: Held usually in October, either in Anchorage or Fairbanks.