Here are the locations for all the Lore and Legend books, along with the level caps for the Lore and Legend quests. A Lore of Legend quest will show up in your journal (and reward experience) based on your level or the level cap of the quest, which ever is lower. So if you read the Gnoll Lore and Legend book at level 10, it will show up in your journal as a level 10 book. When you ding level 11, the quest will automagically show as a level 11 quest. The quest will continue to level up with you until you reach level 51 – as the Gnoll Lore and Legend has a level cap of 50, the quest will not level up with you beyond that. If at level 61 you were to read the book and take the quest for the first time, it would show as a level 50 quest. The level cap is of interest if you are looking to do the Lore and Legend quests for experience rather than simply to gain the Master Strike against that enemy.

This post by Vy shows many locations to find the mobs to gain updates for most Lore and Legend quests.

This PDF by Ripchi offers a tracking sheet for Lore and Legend quest items, especially handy if you are trying to keep track of multiple characters at once. Note the level given on this sheet is recommended level for the mobs needed to complete the Lore and Legend quest, not the level cap of the quest itself. Thus although Orc is cited as level 7 on the PDF and can be completed in Commonlands at that level, it will remain a white cons quest (and reward experience accordingly) until level 50.

Note that Vampire Master Strike is unique in that it is not gained through a Lore and Legend quest but instead is rewarded by completing the D’morte Expansion pack quest line. This is a long-winded quest line aimed at groups in the their mid- to high-30s and requires a pay-for adventure pack to complete.