With Nius Reader you can comment any post, just make sure you logged in and changed your default display name for comments in your profile.
You can open comment dialog by pressing button with comment icon on every post but also you can open post in separate page by clicking post link start with character # in left top corner of the post record. You can keep opened page with post to refresh comments and doing conversation with other users.
You can find your commented posts in Comments page
Have a good chat!