In the Sonar installation process, you picked where you wanted SD content to be placed. On my system, I have SD content stored at: D:\Cakewalk Content\Session Drummer 3\Contents. If you used the default path in installation, it would be at: C:\Cakewalk Content\Session Drummer 3\Contents
You will see folders there for Kits, Patterns, and Programs, and I think the samples are in the Kits folder's sub-folders.
Hope that helps,
Bob Bone