Make a ranged spell attack against the target. On a hit, the target takes 1d10 piercing damage. Hit or miss, the shard then explodes. The target and each creature within 5 feet of the point where the ice exploded must succeed on a Dexterity saving throw or take 2d6 cold damage.
I read this as: where ever the knife lands the original target must roll a saving throw, plus any other creatures caught in the blast radius of 5ft.
Going forward with that I ruled if Ice Knife missed it must land and explode within 5ft of the original target.
Is this correct?
I've also homeruled -with a 5ft grid-: There are total of 4 squares that the ice knife can land: directly behind the target, two adjacent squares (left&right) of that and same square as the target. And roll 1d4 to decide which one it is every time the spell is missed.