For understanding modern Assembler and working with LLVM and JIT, consider these resources:

1. "Programming from the Ground Up" by Jonathan Bartlett for foundational knowledge.
2. "x86 Assembly Language and C Fundamentals" by Joseph Cavanagh offers an in-depth look.
3. Online references like Felix Cloutier's x86 reference (www.felixcloutier.com/x86).
4. Interactive tools, such as jstrieb's ARM Assembly Tetris game (https://ofrak.com/tetris) for practical learning.

These will offer both theoretical knowledge and practical experience.