Where would a raco pkg install --auto drracket install the drracket package by default? This is off of a preexisting homebrew installation of racket.
Try the following to print where your Racket install is installing packages:
Welcome to Racket v6.4.0.11.
-> (require setup/dirs)
-> (find-pkgs-dir)
#<path:/racket/share/pkgs>
-> (find-user-pkgs-dir)
#<path:/racket/add-on/development/pkgs>
(those paths are made up for this example so you will want to actually run this on your machine)
The first path is for installation scope packages, e.g., the packages that come with Racket. The second path is for user scope packages.
If you want to find where a particular package is installed, you can use this package: raco-find-collection