like the -enemy resistance %
how it is applied? my character wearing the jewel passing the effect to summons?

and for that matter how are sundering enemy resistances broken, do they have to be struck by a spell or physical attack from the character or do summons benefit from it also?

They do not not apply to summons or your mercenary. They are part of a damage formula that applies when damage is directly done by your character.

no way for sunderings also?? or just the jewels? my friend made a summon druid and I worked so hard to get us jewels the whole crew lol

Just jewels. Sunder charms do work for summons.

welp, thats unfortunate on the jewels le sigh, thanks for the info though bud