As title asks, it is unclear from the phrasing if this skill does additive or multiplicitive damage.

"10% damage to enemies..."

Does this mean that the enemies take 10% more damage, or is this a relatively weak medium node that just gives additive "+10% damage"?

Typically your phrasing would be "+10% damage if enemies ..." for additive damage, where multiplicitive would be "Enemies take 10% increased damage when..." The way it is worded now is ambiguous. Also, not even sure why they would put that medium node there if it is just an additive conditional +10% damage node, again it seems rather weak if thats the case.