To add a comment to a Wiki Page is required send a comment Atom entry document which includes the comment text. Here's one easy way to do it with an asynchronous HTTP (Ajax) request using jQuery.
There is no a link to IBM Connections 4 documentation.
Atom API Request Details
|Content-Type : application/atom+xml;type=entry;charset=UTF-8|
|Response||Status Code: 201 Created|
Example using jQuery
Note: console.log can throw errors in IE, they are there for illustrative purposes only and should be changed as required.