As you know, package definitions are placed in Guile files. The following commands should help you not get lost in these package locations:
Display a list of files with package definitions. You can press P or RET there to display packages placed in the current file in the same way as M-x guix-packages-by-location would do (see Package Commands). Note that when the point is on a location button, RET will open this location file.
Open a file with package definitions (press TAB to choose a file from the completion list).
Find location of a specified package. This is an Emacs analog of
guix edit command (see Invoking guix edit in The
GNU Guix Reference Manual). As with
M-x guix-packages-by-name, you can press TAB to
complete a package name.
By default, when you should specify a package name (for example, after M-x guix-edit), you will be prompted for it in the minibuffer, but you can configure Emacs-Guix to use a package name at the current point position (unless C-u is used):
(setq guix-read-package-name-function 'guix-read-package-name-at-point)