What is a CSK file
CSK files have been used by the by now deprecated office suite of ClarisWorks. ClarisWorks has been initially developed for Apple computers running on Mac OS and Mac OS X. A version for Windows was released as well. Like any office suite, ClarisWorks contained programs for word processing, spreadsheet creation, painting and drawing, as well as presentation creation.
Not much isn't known about the CSK file extension anymore. The ClarisWorks application is not supported anymore as of 1998.
Here's a small, but not exhaustive list of programs that can open CSK documents: