You would have known if you had bought it - it costs 5 Fieldcraft Demimateria I and 5 Battlecraft Demimateria I. It does NOT cost any HQ Hard Hippogryph Leather. You can even buy it BEFORE you buy your Master Leatherworker I book.

You find the second book under the category "More Items (DoH)" when you talk to Talan.

All items in this book require Demimateria to produce, including the Dodore items you're after.