$ nix-build -A shrunk /nix/store/g9h53c28y71czf94qi3jlm9w527r78b0-linux-4.14.84-shrunk
This is a subset of the module tree produced in the kernel derivation. The subset is specified by the
rootModules argument in stage-1.nix.
That subset is packaged as part of the initrd.
The lis of modules can be extracted with:
$ nix-instantiate --eval --strict -A root-modules