The Rogue's Sneak Attack says
Beginning at 1st level, you know how to strike subtly and exploit a foe’s distraction. Once per turn, you can deal an extra 1d6 damage to one creature you hit with an attack if you have advantage on the attack roll. The attack must use a finesse or a ranged weapon.
You don’t need advantage on the attack roll if another enemy of the target is within 5 feet of it, that enemy isn’t incapacitated, and you don’t have disadvantage on the attack roll.
So my question is can it be used to deal extra damage to objects with normal HP.
The object in question in case it matters is the Soulmonger from Tomb of Annihilation
Best Answer
Sneak Attack only works against creatures
The Sneak Attack feature states:
The feature is described as exploiting a foe's distraction; you can't distract inanimate objects. Additionally the feature explicitly requires you to damage a creature and not an object. Finally the section on when you don't need advantage involves an enemy of your target; objects don't (typically) have enemies. Both the description of the feature and its mechanics prevent it from being used against objects.
That said, your GM may rule otherwise for things such as sentient (animate) objects or even the artefact in question here.