The session manager used by KDE is KSMServer, this tool is used to start all your default applications when you login to your desktop. The session manager is launched automatically by the display manager after login is confirmed.
KDE KSMServer Details
The session manager can automatically reload your last user session including all open windows, or you can choose to run a new default session on every login.
KSMServer Session Manager Configuration Files
Here are some of the configuration files and directories used by KSMSession.
KSMServer Autostart Files
All of your auto-start applications can be found in the following directory as .desktop files. This directory may be different on your system.
KDE KSMServerrc File
Next is the directory for your KSMServerrc file.
Application State Information
Entries for applications specific state information can be found inside the KSMServerrc file as seen below.
Application State Files
You can then find a file for each saved application state entry in the directory below. A file entry for KWin is also shown as an example.