Doggie Language is nonfiction. I bought my copy new.
Review:
This book is primarily illustrations of dog body language, accompanied by short paragraphs or bulleted lists highlighting the important aspects of what you'll see a dog doing and what their body language likely indicates, along with additional details to note (context, what's going on with the rest of their body, etc.).
I'm pretty sure my first exposure to Chin's work was her dog and cat body language posters, both of which are freely available to download and print on her website (along with lots of other really helpful graphics, many but not all of which animal-related). You can probably get a lot of the same information found in this book via Chin's free downloads, but this book has it all in one place, in a format small enough to be tucked away in a bag. I'd have appreciated something like this back when my parents got their first dog. I'd grown up around cats but not dogs - dogs seemed loud and aggressive in comparison, and while I ended up loving my parents' dog, I'm still not always comfortable around dogs in general.
As Chin notes, dogs can have very different body types (curly tails, stubby tails, floppy ears, etc.), which can affect what certain body language details look like. Where possible, she illustrates what certain behaviors might look like in different dogs - for example, relaxed vs. alert ears in a Boston Terrier (upright ears) vs. a Dachshund (floppy ears).
All in all, this is a nice little book, and the illustrations are, as expected, great.