Mostly of the kde-cygwin sources are managed using the sourceforge CVS version control system.
Some of them are located in the projects cvs area, some of them on other places.
The kde1,kde2 and the whole qt sources are located in the projects cvs area, while the kde3 sources are directly used from the kde's cvs server. In this case the patches are located in the snapshots area.
For compiling a specific package see the specific compilation sections of the related package, which can be reached under the topic "packages" on the left side menue.
Now you may follow one of the top links to learn more about how access the cvs repository or to browse the cvs repository online.
Additional see the KDE Code browsing page from developer.kde.org, which may be useful for browsing through the whole KDE code online.
For informations about the structure of the kde-cygwin projects cvs area, see cvs structure.