Important notes:
-Quincy/[Cyte-09] 2nd ability will reload and add the element to this sniper as a second hit with a guaranteed status proc each shot, making modding for elemental status dmg and reload speed a little redundant (raw damage is good though).

-Have 1st and 2nd ability active at all times for max damage.

-2nd ability element selection:
If the enemy survives one hit, pick an element that its weak to for a one shot or pick an element that makes follow up shots' damage higher (Cold, corrosive, viral, magnetic).
If the enemies always dies then blast and electricity might be good for more AOE (Gas only versus corpus). Bonus, electricity stun might help you getting easier headshots/weak point
shots on the other enemies.

-Aura Mod: [Worthy Comradery] (75% weak point crit chance) or [Dead Eye] (52,5% sniper damage). In my opinion [Worthy Comradery] wins, as it works for all weapons for the team and yields more than the sniper damage (above 100% crit chance it will yield between 56.5%-75% dmg increase at all times if it is additive, if its multiplicative... then its way better), only exception might be versus enemies with very difficult weak point accessibility.

-Arcane Crepuscular warframe arcane is solid for this. While invisible gain +30% Ability Strength and +3x Final Critical Multiplier (Ofc when using the 3rd ability to stay invisible).

BUILD
Core:
[Primary Acuity] (strongly recommended) or [Galvanized Chamber] (Primary acuity is a new mod that grants +350% weak point damage and crit chance, but disables multishot)
Spectral Serration OR [Semi-Rifle Cannonade] ([Spectral Serration] is a new mod that boosts dmg by 330% when invisible)
[Critical Delay]
[Vital Sense]

The last 4 slots in order of damage increase:
[Primed Cryo Rounds] (lots of raw damage)
[Target Acquired] (1.6x headshot multiplier)
Primed Bane mod (if you want bane mod x1.55)
[Galvanized Aptitude] (NON Acuity and if using a primer)
OR [Serration] (+48.5%, on NON Acuity only, not if using [Galvanized Aptitude])
[Piercing Caliber] (more raw damage)
[Hammer Shot] (+28.4% dmg increase or there about)
An 11 cost elemental mod (for raw damage or converting cryo to an element with higher dmg multiplier towards your target)
UTILITY: [Sharpshooter] for energy recovery (+15 energy per headshot kill). Depending on your efficiency stat you can literally shoot forever with this and get enough energy for the 1st and 2nd ability.

Additional note:
[Galvanized Scope] cannot be put on this weapon.