Before you can leave to do this Hermaeus Mora himself will appear to offer you to become his emissary by replacing Septimus. You’ll need the blood of every type of Elf, including the Orcs, to open the way so it’s either time to go on a killing spree or simply hold onto it while completing the various quests to get this without undue bloodshed. Septimus gives you an extractor used to take the blood of those you come across to combine in an effort to open the way into the giant cube near him. Return to him with the Lexicon to start up the next stage of this quest, that of gathering the blood of the various Elven races. As this is part of the main storyline it is not covered in this guide. Since it is inscribed by doing exactly what you must do for the main storyline so this requires exactly zero effort on your part. At this point Septimus will give you this quest upon chatting with him, tasking you with inscribing a Dwarven Lexicon for him.

However this quest is started by simply following the main quest until you reach the Elder Knowledge quest. Most of the other quests require that you seek out a particular location or at least visit one of the various towns.

How to become a daedra in skyrim