OK, I see it now you've given directions. Via Firefox, its swamped by the shopping trolley above! It needs a capital A i.e.'Add comment' and some space to make it more obvious. Plus, it only appears if you are logged in, so visitors wont know about it. Would it be better to have it appear to all viewers and then invite them to register if they want to leave a comment?
Still possible. The function is on the bottom of the training page: "add comment". If the newly entered comment does not appear at once, this is probably because your internet browser has a strong caching mechanism and thinks that the content is not changed. If you reload the page the comment will be there.