Actually the "Adds X% to [type] Damage" affix is not grammatically correct. Remove the "to" and it makes more sense. Blizzard confirmed awhile back that the affix adds damage of that type, not
to that type.
So it should read: "Adds 6% Lightning Damage" or possibly, "Adds 6% of your total damage as Lightning damage", how about, "Increases your damage by 6% as Lightning" (I think the last one is the clearest.)
The real tragedy is that, if the SoJ rolled with Wizard affixes, it would couple really well with the Storm Crow. It would increase your damage by 13% and increase your damage against elites by 24%!
Hell, it may still be worth using with the Storm Crow even with the Witch Doctor affixes. Equip them both on a Wiz and see what the damage increase it like.
-420
EDIT: There is an affix that adds specifically to skills that do a certain damage type (like the legendary wand
Fragment of Destiny). For example: "Lightning skills deal 15-25% more damage."