Comment by jsrcout

The Apple II Reference Manual includes assembly listings (with full comments!) for the Monitor ROM and Autostart ROM, the mini-assembler, floating point routines, and a very nice 16-bit "pseudo machine interpreter" called SWEET 16. Most of which was written by Steve Wozniak. Learned a lot from this book back in the day.

Here's a link from archive.org. It's not the best scan, but you can easily find other copies.

https://archive.org/details/applerefjan78/page/n69/mode/2up

If you're feeling adventurous, you can find assembly listings for the AppleSoft BASIC language (though maybe only from third parties). It's pretty huge.