Gallade

Does a Pokemon with multiple types such as Scovillain with the "Double Type" Ability count for two different types of Pokemon for Toxtricity's "Loud Mix" attack?

Yes, Loud Mix checks for the number of types of Pokemon on your Bench, not how many Pokemon there are.

Does Golurk's "Double Type" ability which says "As long as this Pokemon is in play it is both and type" block Flareon's "Flare Effect" ability or Vaporeon's "Aqua Effect" ability or Jolteon's "Electric Effect" ability which adds or or to any stage 1 Pokemon?

No. Golurk would have all 5 types if all of those Abilities were present.

If Flareon's "Flare Effect" ability or Vaporeon's "Aqua Effect" ability or Jolteon's "Electric Effect" ability adds Fire or Water or Electric type to a Darkness Type Pokemon, does Dangerous Energy get discarded since it says, "If this card is attached to anything other than a Pokemon, discard this card"?

No, it is not discarded. Even with the addition of another type to the Darkness Pokemon it is still also a Darkness Pokemon.