Where do you see weapon dmg instead of main or offhand damage? Whatever it is the same thing. Main hand is… Only main hand, offhand is only offhand. (shield or dw weapons). Skills that use both hands will show both main and offhand.
Conversion, there’s probably dozens of sources to look this up. Check the guide first http://www.grimdawn.com/guide/gameplay/combat.php#q20
In this example, the item in question is probably a mythical legendary with a skill modifier, correct?
Conversion is best understood as being a 2 step process, first is conversion from inside the skill, second is conversion from outside the skill. A skill modifier changes the text of the skill, and is therefore from inside the skill (even though the source is an item) and is applied before external conversion.
The flat and %weapon damage will be added before the conversion, so keep that in mind.
It is infrequent with a skill modifier, correct. What are rules for them?
Thank you, that’s what I needed.