Hope said:Weakness and Resistance is always applied before doing damage. In your case, if Zekrom-EX does its Strong Volt on a Kyogre-EX (who has a Lightning Weakness), Kyogre-EX will take 300 damage. However, if Zekrom-EX does its Strong Volt on a Groudon-EX (who has a Lightning Resistance), Groudon-EX will only take 130 damage.
However, in your case, there are also damage modifiers that require Weakness and Resistance to be applied before that damage modifier is accounted for. Take PlusPower, for example. PlusPower adds 10 damage done to the Defending Pokémon before Weakness and Resistance is applied. So, if Zekrom-EX does its Strong Volt attack on Kyogre-EX and a PlusPower has been played, then Strong Volt will do 320 damage to Kyogre. (Of course, you can play multiple PlusPowers at once. If two PlusPower is played, then Strong Volt would do 340 damage to Kyogre.)
But, if a card or an effect reduces damage after Weakness and Resistance (excuse me on this, but I can't think of a good example off of the top of my head), then if Zekrom-EX does its Strong Volt attack on Kyogre-EX and such an effect is on Zekrom-EX or Kyogre-EX, then Zekrom's Strong Volt will only do 310 damage.
Hope, hit the nail on the head with this one . PlusPower is one boost that you will apply before weakness and resistance or else your pluspower may not do what you wanted it to based on resistance or more for that matter . Adding Weakness and Resistance standardly will always be dealt with before your attack .
( I am totally new at this and correct me if I restated this wrong . )
Hope to post more.
~ R-C