If you have Fulfiller permissions in ServiceNow, you have the ability to search knowledge at base level.

• Select Self Service > Knowledge to view portals to each Knowledge Base you have permissions to view.
• Search is available for all bases, or click into a single base to search that base only.
• Search based on keywords found in the article, service, or meta tags. Search is intuitive and will display the most viewed and most useful articles first.
• Each Knowledge Base has a homepage that you can search by Category.

Video Tutorial