Lads,
I have a few (not so quick or easy) questions, regarding damage conversion mechanics in the game. I could not find the information I have been looking for, at least not satisfactorily.
For the sake of the questions and answers, I will pick random examples rather than in-game ones (so the questions and answers will be more general and mechanics-oriented). Some questions may seem easy to answer, others not so much, feel free to pass if you do not know the answer, I would rather have an “I don’t know” than an incorrect answer.
- When an item has, say, “10% physical damage converted to cold damage”, what does it apply to (weapon damage, skill damage, WPS damage, etc.)?
All dmg
- Does the answer to question 1 change depending on what item holds the bonus? (say, if it is on a weapon, does it change the weapon damage, while if it is on an amulet, it changes skill damage, etc.)
No
- How do similar damage conversion stack? For example, if I have 2 of the same ring, and the ring says “10% of chaos damage converted to piercing damage”. Does that mean 20% are converted in total (additive), or does that mean 19% (multiplicative), or even something else (maybe they don’t stack at all?)?
Additive
- Now it gets tricky. If I have an item that converts, say, 100% of physical damage to acid/poison damage on Cadence, as well as a ring that converts 10% of physical damage to chaos, what would be the damage type of Cadence?
About 91% acid and 9% chaos
- Same question than 4, but this time, my ring converts 10% of poison damage to chaos?
100% acid.
- If an item converts 70% of ice damage to aether of Olexa Flash Freeze, and a ring converts 10% of ice damage to aether, would my Olexa Flash Freeze deal 80% of aether damage and 20% ice, or 73% aether and 27% ice (converting 10% of the remaining 30%), or 70% aether, 30% ice (no stacking)?
Shit I dunno. Gun to my head id say 80%
- If I have 3 items, one of them converts 40% ice to aether, one converts 40% ice to chaos, one converts 40% ice to acid/poison, what would be the resulting damage on a skill originally dealing 100% ice damage?
33.(3)% each
- Same question than 7, but this time the last item converts 40% aether to acid/poison?
Aren’t you a curious little bugger. Converted dmg cannot undergo any further conversion
- If I have 2 items, one converts 100% physical damage to chaos on Cadence, the other converts 100% physical damage to vitality on Cadence, what is the resulting damage type?
50/50. This feels like an exam.
- If I have 100% conversion of physical damage to vitality on Cadence, but I also have an item that grants +50% bonus damage to physical damage, does it apply to Cadence before conversion?
No.
- Same question than 10 but this time the bonus damage applies to vitality?
Yes.
- Same question than 10, but instead of 100% conversion of physical damage on Cadence, I have a general 10% conversion?
Why don’t you just ask what goes first: conversion or global %dmg modifier? Conversion goes first.
- Same question than 11, but with the changes introduced in question 12?
Same answer as 11, but with the changes introduced in answer 12 
I may have more questions, depending on the answers. Thanks a lot for taking the time to answer 
Cheers!