Have an empty object variable connected to the Touch event's triangular pin, and connect that same empty object variable up to the target for Cause Damage. Instigator could be the emitter itself.
The damage can be a float variable if you want, but you should be able to define that property's value in the Cause Damage action's properties as well.
Alternately, you could sidestep the Touch event and place a physicsvolume where you would receive damage from this emitter, and set up Pain Causing and damage amount in its properties.