A possessive contraction ending in s can be spelled either way. It's not the most common usage, and definitely not the easiest to pronounce. But, it's still correct english on a technicality.
English
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Only if the object possessing the item is plural James' book (book owned by James) James's cinema. (Cinema owned by 2 or more James) Just like you can't really plural the names either 1 Jack. 2 Jacks 1 James. 2 James So Skolas's is only correct under the pretence that there is 2 or more Skolas.
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Or if the subject is his revenge and he has multiple things to be vengeful for. English can be turned every which way. It works either way.