Use UNIT_SPELLCAST_SUCCEEDED to determine when you have cast disenchant or prospect:
http://wowprogramming.com/docs/event...CAST_SUCCEEDED
Use ITEM_LOCK_CHANGED to determine what item was targeted:
http://wowprogramming.com/docs/events/ITEM_LOCK_CHANGED
Use the loot API to figure out what you have received:
http://wowprogramming.com/docs/api_categories#loot