Use the catalog "Effect" type. You have to reference the effect that handles the damage for a weapon ("Amount", field). For the period, you have to reference the weapon itself.
If you're confused and need specific instructions, I'll follow up shortly.
As said above, damage is not on the unit, it is an effect. The easiest way to find what you are looking for is to click on it in the data editor. Then (i forget which tab, VIEW i believe) click "view as raw data". all of your fields will change to be what you would want to put in that function...
Say "Zealot Attack (damage)" was the name of his attack effect, it would most likely be affect;ZealotAttackdamage;Amount