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.
English
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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.