I searched all the thread on Demonic Sac. and Demonic Knowl but nothing came up so if this is posted before please link and ill hand all credit to them.
Ok so first an explanation of how the spell are suppose to work. This works best in instances but can be done in Nagand easily and any other place enslavable demons are easily accessed.
Demonic Knowledge- Demonic Knowledge - Spell - World of Warcraft
Pretty simple you get whatever % you spec from your pets int and stam.
Demonic Sacfrifice Demonic Sacrifice - Spell - World of Warcraft
You are only suppose to keep the buff until you get a pet which is what is exploited in the end.
Simple enough summon a demon up and use Demonic Sac. Whether you want Succy for damage or whatever its all good. Then find the demon you want. Demons with high stam and intellect will give you the best bonus spell damage. Enslave it and check your buffs. You will still have Demonic Sac but also have Demon Knowledge! Demons in heroic Blood Furnace can almost give 300 bonus damage. That plus a 15% shadow damage is very nice.
This was apparently suppose to be patch but last time i tried it worked so i guess it wasn't.
Also one last thing i wrote this while doing SSC so if there is any errors or whatever sorry ill fix later.