Unfortunately Tome of Obtenebration does not exist on Single-Player only Multiplayer.
BUT there is a way you can get it, after my fifth play through I always added the item to my inventory and used it on Willhem.
You have to enable console then write:
and then press enter
and you will have it summoned on the ground. pick it up and use it.
But I have to warn you, Obtenebration is flawed, you can only use 1 level. I suggest you to use a mod for it to expand it. there is a mod called "Within the Darkness" that has alot of new disciplines, that can be fun but I suggest that only after your first play through is done.
--PS-- you should have set the thread as "Question" -- it would be more fun answering it.
Sorry didn't think to set that. And Thanks for the answer :D
So there are more Disciplines?
There is a mod called "Within The Darkness" that adds almost ALL the disciplines, and reconfigure the ones already in, but I dont suggest to use that until you finished the game at least once or twice. and the game is varied enough for you to play at least 7 times. and btw it has 3 possible endings.
Other disciplines NOT found in single player are not many, in fact I can remember these are all of em:
Faith -- Human Only
Hands of Destruction
Lure of Flames
Numina -- Human Only
The one that you wont find is "Dementation", you can summon it by its name:
btw. if you like press a +1 on the post, the list was not easy to come by (^_^) and in Alphabetic order even (-_-)
If you have more questions, please, let me know.