It is not possible to make Articles Versionable in the current release of Service Desk, however, it's on the plan for the next release (7.8.2, due early July). If you'd like to take a look at the features now, you can download the latest Beta of the software from http://servicedeskbeta.landesk.com.
I understand that versioning of articles is planned for v782.
However, if you have a real need for this before then you could consider using a Configuration Item that has version control enabled. You could then link that to your article and use that as your version control. My advice - unless this requirement is needed now - would be to wait until early summer for v782 and use the functiionality directly within the knowledge domain.
thank you for your reply. I will wait till version 7.8.2 is out.