There are no staffs. Other than the bonuses, or as a backup for close quarter fights, there is no particular benefit to equipping a sword and shield for a mage.
In DKS duel wielding is quite effective for a mage. The magic damage bonus/enchantment of both weapons is applied to spells (including each missile in a Magic Missile volley). There is no need to boost the duel wield skill if you are not going to engage in melee combat, as the off-hand weapon penalty is not taken in to account for spell damage.
You should be able to see the formula in your inventory. There is no way to check the ones you have other than by talking to an alchemist (I kept a written list handy when I played, to keep track of the potion and enchantment formula I had).
