I have seen people recommending this book: "Mac OS X Internals: A Systems Approach" by Amit Singh. It's a bit older and includes PowerPC stuff, but a lot of things really haven't changed in OSX internals. I haven't read it myself.
Another book I have seen people recommending is "Mac OS X and iOS Internals: To the Apple's Core" by Jonathan Levin.
And Apple itself has a lot of internal documentation available on their site. It's sometimes hard to find, but there's a lot of good stuff out there:
https://developer.apple.com/libra...ernelProgramming/About/About.html