Using CLI tools
As indicated by derobert, Debian packages which are maintained in a VCS are supposed to indicate this in a pair of Vcs-... fields in their source package.
The best tool to use this information is debcheckout in the devscripts package, or apt-cache showsrc. Both of these will show you gnome-disk-utility's repository information.
apt-getcache showsrc gnome-disk-utility will show all the information contained in the source package, including links to the VCS (Vcs-Brower gives a link for use in a brower, Vcs-Git give the link to clone the git repository, assuming the repository uses git):
Vcs-Browser: https://anonscmsalsa.debian.org/cgit/pkggnome-utopiateam/gnome-disk-utility.git Vcs-Git: githttps://anonscmsalsa.debian.org/pkggnome-utopiateam/gnome-disk-utility.git whereas
debcheckout -d gnome-disk-utility will only show the VCS information and pertinent details (if the package is hosted in a VCS).
Checkout
If you then want to check the source out,
debcheckout gnome-disk-utility will do that for you.
Web Interface
You can also see this information on the Debian Package Tracker, which will link to the VCS where the package is hosted (if there is one).