There is only one file type that uses the .MSKN extension:
MediaMonkey Skin File
Theme, or skin, that defines the look and feel of MediaMonkey, a program for organizing and playing music files; contains interface settings for the title bar, status bar, buttons, tabs, and checkboxes.
The default MediaMonkey skin file is named "Theme.mskn," which can be edited with the KSdev theme editor.
Updated: June 20, 2008