Urgot's W

Will it proc' on hit passives/abilities?

Yes, but on-hit effects that deal damage will only deal 33% normal damage.

If yes, will it scale in attack speed if you have a ?

No, Urgot's W will not scale with attack speed. I have not tested if it will proc on-attack effects like Guinsoo's however so that it can at least stack the item. I know it procs Runnan's Hurricane so it might be worth checking out.