Basically ToK is a book that keeps track of everything your character does ingame, and you can go and read about your adventures, what places you visited, what mobs you killed, titles, achivements, etc... its basically your own encyclopedia.
Warhammer failed in various parts, but the one thing they did right was ToK, and it amazed me that no other MMO since tried to introduce such a feature, maybe its a very big feature to be made and dev just decide not to do it. All i know is that this should be in my eyes a feature every MMO should be introducing to their game. Blizzard only introduced achievements because ToK add them, they thought it was a good idea to have in WoW, just a reminder that ToK only had 3 Tabs at launch and nowadays it as around 10 tabs.
For the people that never played WAR, here are a few links that some waht explain what ToK really is and its Huge Potential to be a great feature in TESO
Short Basic Video - search on youtube for mKLNQkjT0n0 - only up to 4m40sec
Wiki page - warhammeronline dot wikia dot com/wiki/Tome_of_Knowledge
ToK written Guide - ageofreckoning dot warhammeronline dot com/TomeofKnowledgeGuide
if you google Warhammer Online - Tome of Knowledge Explanation p1 to p3 you can find the WAR devs explaning it in depth (remember its was for the first iteration of 3 tabs)
So what you think, Would TESO be more rich if they included such a feature?