Current State:

It is possible to link both Internal and External Confluence Knowledge Base spaces with JSM. From an agent perspective, however, it is only possible to search for External KBs using the "Suggested Articles" feature in the Jira issue view.
 

Proposed Future State:

To enhance efficiency, it would be useful to have Internal KBs included for agents when using the Jira issue view's "Suggested articles" search.

Workaround

Currently it is possible to access these articles by navigating to the "Knowledge base" tab using the left-side navigation bar.