@shegeley I just use (asdf:load-system :package-name) and it just works if the package is installed from Guix. Afaik I don't have any special config apart from the path etc. environment variables described in the manual.

For personal projects I add the project directory to the ASDF search path before running the load-system function and it just works as well.

Not sure if this plays well with e.g. Quicklisp though.