Getting the Vkd3d source
You can download the Vkd3d source code as a tarball), but if you plan to do any actual testing or developing, you'll want to use git. For more information and some useful hints, see GitWine and the SourceCode wiki page.
To grab the source code to wine itself, just enter the following command, replacing the directory path at the end with whatever folder you want to download the source tree into:
git clone git://source.winehq.org/git/vkd3d.git/