One Configuration Item, (CI), can be associated with a single Knowledge Document.
Open a Knowledge Document in Edit mode, click the tab Document Access and then Attributes, you will see the following fields;
One CI can be set on multiple Knowledge Documents. The following image shows the Knowledge Management tab on the detail of a CI.
The Knowledge Search on this page is only for searching of Documents already associated with this CI, this search is not a search of your entire Knowledge Base.