A book about croissants/viennoiserie
I'm actually surprised that there is :


Celebrating Croissants: 40 Fabulous Fillings for National Croissant Day - Ideal for a Bistro Breakfast or Light Lunch


Your other option might be to go for a more generic one on French pastries:


Bake Like a French Pastry Chef: Delectable Cakes, Perfect Tarts, Flaky Croissants, and More


I'm not familiar with either of these, but the second one reads like a text book ... glossary of terms, explanation of ingredients, step by step instructions, and lots of pictures.  (although 'Look Inside' didn't take me to the puff pastry or croissant chapters, and Amazon didn't OCR the book, so text searching won't work).  The first one Amazon doesn't have a scan of, so I have no idea how much detail it might have in it.