In the Silversky Palace, find Tobias (he is a mage near the palace dungeon). Say “Book of Warfare” and “Yes” and he will sell you one for 15.000 gold pieces. Take the book to Adriana (she is the armor penetration teacher east of the pot shop). Say “Book of Warfare” and she'll agree to trade it for the Blade of Sharpness. Say “Yes” and you'll do the trade.

Note: You can do this quest as many times as you want

NPCs involved: Tobias, Adriana

Quest Reward Synopsis: Blade of Sharpness