AK,
The only available way to comment with LinkedIn is using the LinkedIn Share button. When you click Share, the user can also type in a message that will be posted with the shared link. The user will be required to authenticate on your site first with LinkedIn before the Share can go through.
To configure LinkedIn Share, you can:
1. Enable the JFBCContent plugin and configuring the Share setup in JFBConnect > Social > Content Plugin - K2 Like.
2. Add an instance of the SCSocialWidget configured to use the LinkedIn Share widget.
3. Or add the {JLinkedShare} easy tag to your page manually.
I hope this answers your question, but let me know if you need more clarification.
-Melissa