Abah's Watch Style is a collection of 14 books that make up part of the Crafting Motifs library. Reading the chapters teaches you the Abah's Watch Style for crafting. Chapters (or rarely the entire book) can be found as a possible quest reward for completing Thieves Guild Tip Board quests at the highest tier of rewards. (Large Laundered Shipment) The complete motif book is a legendary reward in Hollowjack Crown Crates.
Learning all 14 crafting motifs earns the achievement Abah's Watch Style Master.