Thanks for your question. I'm not aware of a plugin (or another Joomla extension) that currently exists to show someone—the site administrator, perhaps—a count of the what message attachments in
Kunena people may be downloading (for example, PDF or ZIP files or anything else for that matter) or the number of times those attachment files have been downloaded from your website.
There are, however,
other file repository tools for Joomla (search the
other file repository tools for Joomla
for "download control"). Instead of using the "attachments" feature in
Kunena, you could upload your "downloadables" to a "file repository" and reference them with links in a forum message. Most of the "file repository" products that I've used allow you find out how many times people have downloaded files from your website.
Another suggestion is to use some analytic tool—e.g
Google Analytics—(perhaps you could set up a filter) to see what files are being clicked on.
But, in simple terms as far as
Kunena (specifically) is concerned, I think the answer to your question is no.