Freya Necklace + Wynn

Would freyas magic skill -5% cooldown be noticeable in wynn for marks? and would that affect my reapers magic skills as well?

Yes it will help.
The stats do not directly apply to summons so no. The only thing that directly transfers to summons is element the rest is only transferred through servitor share.

What would you say is better for Wynn, Frintezza or Freya??

Freya. The M.Def difference cannot be ignored.

WTS Frintezza then :D:D

what Boss Jewels useful for Wynn?

Freya (or Blessed is even better)or if u want to be more dd then can try Valakas.
Zaken+ Antharas due to resists and mental attack (ofc both blessed are beter, but its way more expensive option).
And for rings only quitecheap/usefull option is Istina (that 54.4 crit rate improves ur dps with coguars). Ofc u can try to get earth wyrm due to resists/mental attack and m def.. or Beleth (mental attack)but ts close to immposible :) And ofc tauti is fine as well - high m def, good resists, pvp atributes,but there are no tauti rings in all NcWest serwers i think :)

I think that Ceremony of Chaos' earrings are a better option than normal earring of zaken/antharas, since they have quite more mdef and give other bonuses as well.

but there are no tauti rings in all NcWest serwers i think :)

This ring exists on Naia.