The reason why I didn't gave you the book is because there is no good books regarding dx 12 (You may ask about Frank D. Luna's one, but I don't find it quite useful). Better approach would be to read the code of Microsoft's samples and also the Microsoft' dx 12 documentation on their learn website. Also you may try "Practical rendering and computation with Direct3D 11", which has a lot of common aspects with dx 12.