@Ankur Bawiskar , 

Yes, they can see the Attach button, and once an article is attached, it changes to "Unattach." The following message is displayed at the top of the form: "Details of 'Knowledge Article' have been added to the Additional comments (Customer visible) field."

PS: If I create manually a new article from the Attached Knowledge, it is created in the "kb_knowledge" table and the Source Task field is populated with the HR Case number.

Best regards,
Victoria