How Crown of Eyes work?

I can't understand. For example i have from tree "+% spell dmg", and use skill cyclone
"Increases and Reductions to Spell Damage also apply to Attacks" apply to which part? Is it increase physical damage?

No, to all damage, just swap 'spell' in bonus description for 'attack', so 'increased spell damage' becomes 'increased attack damage', and 'increased elemental damage with spells' on Elemental Dominion notable becomes 'increased elemental damage with attacks'. Such general bonuses are really rare, there's only one on the whole tree, I think, it's Graceful Assault notable near Point Blank. There are a few similar nodes at shadow and templar area but those are restricted to melee.

A regular attack build won't benefit too much from it as spell damage bonuses aren't overly common on the tree and are concentrated around north side. You could get 100% increased attack damage from shield and doedre gloves but using crown and doedre means two items with pretty much no defenses. Attack builds rarely have damage scaling problems, damage nodes are strong and plentiful so the best case scenario for crown of eyes and a purely attack build would be a crit build with some ranged skill, those typically have less increased damage investment and can handle being a bit squishy.