I have played Titan Quest v 1.08 for quite a long while now, and I have wondered whether Weapon enhancements (via skills : Envenom weapon, Storm nimbus and Earth Enchantment, with it's upgrades) affects the damage of regular spells of the same element.
For example, will spending points in Toxin Distillation (level 16 Rogue mastery skill, upgrade of envenom weapon) Affect the damage of Poison gas bomb?
Yes. As supported by this Q&A thread created by a member of the Titan's Quest staff:
Modifiers to damage types from an item, an active buff (Call of the Wild), an active aura (Earth Enchantment, etc), a self buff (Blade Honing, etc), an unattached passive skill (Anatomy, Volativity, etc), and all three of your attributes affect ALL types of that damage. Generally, the only types of modifiers that do NOT affect all types of damage dealt are the passive modifiers to base skills, such as the damage bonuses to Ice Shard or Flame Surge.
That means your sword hit, your staff shot, your bow shot, your spell, whatever. If the damage types match up, they get boosted. +25% Fire damage from a ring? More staff damage if your staff deals fire damage. More fire damage from an axe with fire damage on it. More fire damage from a spell that deals fire damage. Same for any of the other modifiers. The only exceptions are the specific cases where Str or Dex do not boost some skill damages, or amplify the effects of +flat damage bonuses from equipment.
There is also this thread with gamers saying the same thing:
All % mods on all gear affects all attacks that have that attribute. +% Elemental damage applies to all Intelligence based attacks which I believe includes Fire, Frost, Lightning, Burn, Frostburn, and Electrical Burn.
It should also be noted that any +% DAMAGE bonuses means physical damage only, which was also stated in the above Q&A thread:
+% Damage is PHYSICAL damage. Other +% damage types list the specific type (+% Bleed Damage, +% Poison Damage, +% Fire Damage, +% Life Leech, and so on)
