Atemsis, All-Seeing and Mask of Immolation interaction
No, it doesn't. While it's certainly Atemsis, All-Seeing who does the damage (so a Circle of Protection: Blue would work to prevent it), the damage is done at a moment when Atemsis, All-Seeing is in the graveyard (it has been sacrificed as part of activating the ability). It has the reveal-your-hand ability only when it's on the battlefield, so it won't trigger.


  113.6. Abilities of an instant or sorcery spell usually function only while that object is on the stack. Abilities of all other objects usually function only while that object is on the battlefield.


A list of exceptions follows but this ability is not one of them.