1) You can find Leandra's blood in the Immaculate cathedral. It looks very similar to a health potion and is a regular inventory item.
2) You have to combine the spell and the blood in a normal crafting process to create a spellbook.
3) It's a special spellbook that doesn't vanish and has no skill requirements. So every member of the party can learn the skill to make Death Knights vulnerable.
4) Yes, you will be able to kill every Death Knight apart from the few in the mine since the mine collapses once you left it throught the old temple. You just have to use the skill you learnt from the spellbook like a normal spell to make the knights vulnerable at the beginning of each fight.
Last edited by LordCrash; 11/07/14 04:01 AM.