General

[quote=TheGr3atSnakes]Strong Body Strong Body: The harmony of the power of the spirits is imbued within your body, permanently increasing your defense, magic defense, and resistance to statuses and elements. (required skill: 20 Body Trinity) (max level: 10)
Level 1: 550 defense and magic defense, 13% resistance to statuses and elements.
Level 10: 1000 defense and magic defense, 40% resistance to statuses and elements.[/quote]

The 40% resistance in this skill is your own ability to help block status problems like stun/seduce/darkness/etc.
It has nothing to do with the elemental resistance some bosses have which halve your damage.

[quote=TheGr3atSnakes]Eunwol has a 3rd job skill that ignores elemental resistances by 40%. Does that mean I'll do doing 40% more damage on a boss like hilla if I had 0% ignore elemental resistance?[/quote]

Eunwol does not have a skill like that.

Imagine attacking a Fire type Pokemon with a Fire type move.
It's not very effective, right?

Now imagine attacking it with something neutral, for example, Electric. You'll do normal damage.

That same principal applies here. Not type resistances, but just resistance as a whole. Bosses are formidable creatures, and therefore have gained resistance to attacks. So if you can break that resistance, you'll be dealing your normal damage, aside from some other factors such as %PDR and %Boss.

Elemental resistance is the whole , while Physical resistance is one of the properties that elemental resistance can have. So yes, increasing your elemental resistance ignore % will also affect your physical resistance ignore %.

Elemental resistance is the general term, physical resistance is when a boss resists physical attacks. The only way to do normal damage is to have an elemental reset skill that ignores that resistance, or raise up insight for the small ignore elemental resistance it gives.
Before, some bosses and enemys resisted some elements while were weak to others, but now a days most bosses resist every element including physical.