Enemy Damage types

You are right, the wiki lacks the info in most cases. There are a few enemies that do have their dmg type, but, it's few and far between. Like everyone knows vaettir in melee do earth, raptors are slashing, anything bow range is usually piercing (except spirits are light iirc)...

It's usually just noted on pages of stuff ppl farm a lot I guess.

Testing the elements can be done with the mesmer skills "Mantra of Earth/Flame/Frost/Lightning" and just look for energy gain from the skill.

Piercing/Slashing/Blunt can be done by checking for dmg reduction due to insc on shields or if a +10 armor difference isn't enough to tell use an assassin for infiltrators / vanguard / saboteurs.

The elements could also be tested with armor bonuses / look for less avg dmg too, but, the mantra method is much easier.

Edit: And if you figure out dmg types for things and its not in the wiki, plz add it there!