Hey Christina,
I actually just installed CJBlog & found out that it actually uses com_content (article manager) and on my joomla installation I can see the comment form below the blogs:
awesomescreenshot.com/0f71h6nx6d
So, it must be something with your configuration. Can you provide me with backend access to your site?
You can also make sure that content - ccomment plugin is turned on and commenting on com_content is allowed in the parameters of that plugin.
Also you have to make sure that in Components -> CComment -> settings you have created a setting for com_content and that you've allowed the correct categories to comment on.
Regards,
Daniel