You can define a template for articles that are created in a knowledge base. The author has the option not to apply the template, though, so this might not be the ideal solution if you require all articles to be assigned to a particular group.
An alternative to this could be a client script that auto-populates the ownership group field when the knowledge base field changes. You'd have to take into account creating the initial article (from a template) as well as modifying an existing article. Furthermore, if you don't want people to update the ownership group, you could set the field to read only.
Or, in the ownership group dictionary entry, you could set a dynamic default value. I've not worked with these so can't give you any advice there.
