I can't find ondamagescript so I doubt that we have that but we do have takedamagescript which has these:
self: Caller.
attacker: Entity causing damage.
damage: Amount of unmodified damage.
attacktype: Type of damage.
drop: Knockdown power of damage.
noblock: block break force of attack.
guardcost: Guardcost of attack.
jugglecost: Jugglecost of attack.
pauseadd: Pause value of attack.
You can call the variables on the left to get their value