If you make a Physical (Forcewave) build then you usually go as much Cunning as possible.
Cold Forcewave - it depends on details of your whole setup, I’d go Physique or Spirit.
I say totally depends on which you focus more. Seeing you take star pact, I say go all the way cold, the same goes for devotion. Then look at HP and DA, I play comfortably at least at 12k health and 2.8k DA, so the stats go physique until I met the number, then the rest go spirit.
Damage ratios shouldn’t be what you’re looking at when thinking about this. It’s whether you’re making a character around dealing as much Physical/Internal Trauma, Pierce or Bleeding damage (in which case, go Cunning for more +% damage to these) or Spirit for a character around Fire/Burn, Cold/Frostburn, Lightning/Electrocute, Elemental, Acid/Poison, Vitality/Vitality Decay, Aether and Chaos damage for a bigger +% damage to those.
I’d hope you’re not making a character for Physical damage as converting 60% of your damage away into Cold is a massive damage loss .
Finally, it is worth going over stat priorities - only go for excess Cunning/Spirit when it is safe to do. There’s not much of a point going after more damage if you can’t stay alive to begin with to deal your bigger damage out. Have some defenses you can rely on (e.g. damage absorption/enemy damage reduction) and suitable amounts of health, armour, resistances, strong health recovery etc. first.
The reason it’s recommended to go most/all Physique for new players is that it’s more comfortable to have the extra Defensive Ability/Health as an extra layer but experienced players can readily start to sacrifice it when they know how much they need at a minimum to handle specific fights, when to use temporary defenses like circuit breakers to maximum effect and can build up strong layers of damage mitigation in other places than just Defensive Ability.
If I were to level Cold Forcewave, I’d probably play Nightblade (so Blademaster) and then I could farm Alkamos’ Scythe
which would give me 100% Physical to Cold (50% from skill mod to Menhir’s Bulwark and 50% from a prefix + native weapon’s conversion).
If I’m not mistaken @Relinfearous did this meme some time ago.
Would recommend against raising both Physical and Cold damage simultaneously in favour of specialising in just one (like what tqFan suggested above for pure Cold) but I can’t stop you. Sometimes, you learn what works best by trying things out and seeing what sticks and doesn’t stick.
so for example IF i have piercing> cold conversion on items Silver Sentinel’s Mask does it affect nemesis attacks?
fast google looks like - yes.nemesis will convert piercing atacks to cold
Battlemage, Level 100 (GD 1.1.9.5) - Grim Dawn Build Calculator 
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