- Hermaeus Mora - The Elder Scrolls IV: Oblivion
Location: In the mountains far west of Bruma.
Requires: Every other Daedric Shrine quest complete.
Level Requirement: Level 20
Reward: Oghma Infinium
Once you have completed every other Daedric Shrine quest, you can then take a quest from the Daedric Lord Hermaeus Mora. After completing every other Daedric Shrine quest, have your character sleep in any bed. When your character awakens, you will find yourself face to face with a man named Castas Falvus, who explains that you've summoned by Hermaeus Mora.
It's quite a trek to Hermaeus Mora's Shrine. The shrine sits high up on a mountain, but there is a trail that leads right up to it. The trail starts a little west of Bruma (west of the 'B' in the 'Bruma' text on the world map), and is just a bit south of Echo Cave. The start of the trail is lined with rocks, so you should be able to determine where it starts. When you have found the start of the trail, follow it all the way up to the shrine. It may not seem like it, but following this trail will indeed take you to the Shrine.
Hermaeus Mora's Shrine is high up in the mountains west of Bruma.
Approach the shrine and summon Hermaeus Mora. If you meet the requirements, the Daedric Lord will give you a task. Hermaeus Mora provides you with a special spell and Soul Gem; with Mora's Soul Trap spell and Hermaeus Mora's Soul Gem, you are tasked with capturing ten souls, one of each race. To capture a soul, all you must do is cast Mora's Soul Trap on a target, and then kill them. The soul will be placed in Hermaeus Mora's Soul Gem, and a journal entry confirming the capture of a soul of the target's race will be added.
Capturing a soul of each race is not a difficult task if you are not opposed to murdering innocent characters. You can likely find at least one character of each race in each of the major cities. It would be best to refrain from doing this, however, as it is possible to kill some quest givers. Another option is to travel to other Daedra Shrines and capture the souls of the followers there, since they won't be needed for any quests in the future.
Perhaps the best way to go about completing this quest is to capture the souls of Bandits, Marauders, and other human enemies. Bandits can be Khajiit, Redguard, Wood Elf, or Dark Elf; Marauders can be Argonian, Orc, Imperial, or Nord, and Necromancers can be High Elf, Imperial, or Breton.
Capture the souls of Marauders and Thieves in Rockmilk Cave, which is along the western road leaving Leyawiin.
Bandits are usually encountered in camps, or randomly on the road. Fast travel to several different camps and you should be able to acquire the soul of a Khajiit, Red Guard, Wood Elf and Dark Elf. A good place to search for Marauders is Rockmilk Cave, which is north of Leyawiin. To find it, travel north along the west road leaving Leyawiin until cave icon appears on your compass. Inside, you shouldn't have difficulty capturing an Argonian, Orc, Imperial and Nord soul. As for High Elves and Bretons, you'll have to visit a Necromancer lair. One such spot is Fort Linchal north of Kvatch. Just travel north from the 'h' in the 'Kvatch' text on the world map.
By traveling to Rockmilk Cave and Fort Linchal, you should be able to capture a soul of each race. When you have all ten souls, return to Hermaeus Mora's Shrine and give him the packed Soul Gem.
For completing the task, Hermaeus Mora rewards you with the Oghma Infinium, a special skill book. When this book is read, you'll be given the option of reading the Oghma Infinium in a certain way. There are three choices: the Path of Steel, the Path of Shadow, and the Path of Spirit. Each path raises three different skills by 10 levels, as well as one attribute. The Path of Steel raises the Blade, Heavy Armor, and Blunt skills, and boosts the Strength attribute. The Path of Shadow raises the Sneak, Security, and Light Armor skills, and boosts the Agility attribute. The Path of Spirit raises the Destruction, Conjuration, and Restoration skills, and boosts the Intelligence attribute.
Read the Path that will boost skills relevant to your character.
It would be best to refrain from reading the Oghma Infinium until you've maxed the skills that would be raised by reading the Path of your choosing. By doing so, you can permanently exceed the skill level cap by 10 for those skills.