Cocoa Powder or Powdered Chocolate doesn't really spoil or go bad at all and can last a long time.
However overtime the powdered chocolate or cocoa powder can become hard and lose it's potency and flavor but the cocoa powder or powdered chocolate will remain safe to consume.
Powdered Chocolate or Cocoa Powder has a shelf life of around 3 years and after 3 years the powdered chocolate can become hard and the flavor gets less tasty.
But you can always smash up the cocoa powder or powdered chocolate to get it back to it's powder form or run the powdered chocolate or cocoa powder through a coffee grinder and it will turn back into powder.
As long as you keep the powdered chocolate or cocoa powder out of high humidity or away from moisture it should be okay and last a long time.