In scenarios, in which you want to print a particular container on the page (be it a Window widget or anything else), you have two options:
1. CSS-only solution
Use a print stylesheet
and hide everything on the page, except the contents of the Window widget. This contents is inside a <div> element with the Window ID
(Name) and a .k-window-content
CSS class. This option is viable, if the user will never like to print anything else from the page.
the Window's contents inside a new browser window and print that window. The documentation shows how to do that with the Grid. Your scenario is a lot simpler, so your will need to remove most of the custom CSS and JS code.
Check out the Telerik Platform - the only platform that combines a rich set of UI tools with powerful cloud services to develop web, hybrid and native mobile apps.