Contacts are not my strong suite, but here is how my conacts are listed the "Userdata" subdirectory in SK98 (I'm sure it would be the same in SK99):
*.sk*
*.sk1
*.skcard
SK also creates temp files of contacts in the Userdata subdirectory. Currently I also have a *.sktmpcard file.
Hope this helps. P.S. I own both SK98 and Sk99. Even though I bought and paid for SK99, I've gone back to using SK98 as I found the software much more user-friendly than SK99.