The DC is 10 + casting stat bonus + spell level + feats and/or equipment + etc. That's not a riddle. The saves work the same way. Neither is static since both are dependent on variables among players and enemies and we just compare the too then toss in some luck.
Are you saying you want the different DC's posted for every spell and/or ability each enemy on the screen has? Or just a database of mobs with the DC's posted?