You can do it like this:
- Go to the KB, and open the article you want to link to. Click on 'Direct link' and copy the URL named "For internal KB links". You might need to first click on 'Show article info' to see the 'Direct link' icon.
- Navigate to the article where you want the link, and edit it. Write the text for the link, mark it, and select link icon in editor.
- In the link dialog that shows, paste in the copied URL in the 'Link URL' row.
- Save the link, and then save the article.
Now,when you click on the link, it will open the linked article in the content frame of the KB.