Talk:Expose Weakness/@comment-25308694-20140815165005/@comment-24385282-20141109010527

Look again. This means that if Leona damages an enemy with one of her spells, they recieve Sunlight, and, if she has a point in Expose Weakness, she applies that damage buff as well. This means the first ally to deal damage to that target within 3.5 seconds will consume the Sunlight debuff to deal 20/35/50/65/80/95/110/132/140 bonus flat magic damage (depending on Leona's level), and all ally damage to that enemy within 3 seconds deals 1% increased damage.

This additionally means that the first ally to damage an enemy that Leona has damaged with a spell will deal:

((The damage from that item effect/Summoner spell/ability/basic attack)+(The amount of magic damage that Leona's Sunlight deals based off of her level))*(0.01)+(The damage from that item effect/Summoner spell/ability/basic attack)+(The amount of magic damage that Leona's Sunlight deals based off of her level).

Or in other words, yes it indeed does scale/stack with Leona's passive.