Reddit reviews The RISC-V Reader: An Open Architecture Atlas

If you're a complete beginner with assembly language then this book is a gentle introduction to RISC-V. https://www.amazon.com/RISC-V-Assembly-Language-Anthony-Reis/dp/1088462006

However it covers only a part of the instruction set and uses its own non-standard tools.

If you're experienced with assembly language on other ISAs then I'd say just dive straight into the Instruction Set Manual https://content.riscv.org/wp-content/uploads/2019/06/riscv-spec.pdf

The problem with reference manuals is they explain how every instruction works, but don't give examples of how to combine them together into useful programs.

The "RISC-V Reader lies somewhere between: https://www.amazon.com/RISC-V-Reader-Open-Architecture-Atlas/dp/0999249118

I don't know of any tutorial specific to the K210 or MaixDuino. The MaixDuino, as the name suggests, comes with software plug-ins to let it work in the Arduino IDE, so all or most standard Arduino tutorials and examples should work. However of course these are in C++, not assembly language,

Try the RISCV reader book. It’s pretty good, even if the privileged section is somewhat out of date

EDIT: link to book https://www.amazon.com/RISC-V-Reader-Open-Architecture-Atlas/dp/0999249118