Depends. The Scion's shockwave only hurts you if you're exposed when it passes by. If it's unsupported simply stay in cover and whittle it down. Sniper Rifles, Heavy Pistols, and Assault Rifles pack a good punch against armor and will drop it pretty quickly. Warp, Incinerate, and damage boosting powers like Tactical Cloak and Adrenaline Rush will help tremendously. Duck back into cover when it fires to avoid damage by the shockwave attack and then just rinse and repeat. If the Scion has support it will be trickier. If it's supported by Collectors the same strategy as above will apply, just keep an eye out for Harbinger. If supported by Husks, try to strafe back and forth to dodge the shockwave. It moves slowly so you can avoid it. Take out the Husks then head into cover to deal with the Scion.