Probably the most straightforward route is to choose a system of this type—-either a Lisp or a Smalltalk implementation—-and learn how it behaves.

The source code for both Lisp and Smalltalk implementations is readily available, but may not help you all that much until you’re at least generally familiar with what the features are and what they do. Once you’re familiar with their behavior and with reading Lisp or Smalltalk code, then you can start rummaging through the code and asking questions of the implementors. Implementors of Lisps like CCL and sbcl, and of Smalltalks like Squeak and Pharo are pretty accessible and generally pretty friendly, and they certainly know how the systems work.