data\weapons\weapons.
(this is just an example!)
Code:
<wand id="8910" level="42" mana="13" [I]min="55" max="75"[/I] type="death" function="default"> <!-- Underworld Rod -->
<vocation name="Druid"/>
</wand>
there you have
min="55" and
max="75" damage of the rod. Other rods (and wands ofc) are in weapons.xml too.