First, you need to register on that site to post a comment, once you post it, look at that page source code, as an example, I will take a screenshot of THIS page (this one on WJ), to show you how:
In Google Chrome, left click on link, when you see the menu, click on " Inspect element", and you will see something like this:
If you see rel="nofollow" then link is nofollow, if there is nothing, then it's dofollow.
On a same page, some links can be dofollow, and some nofollow. Depends on lot of things, where link is, and how webmaster wants it to be.
For example, on that particular page, Guest links are dofollow.
But that particular page doesn't have PR8, it has PR0, so it won't pass PR juice to you. If your link was on front page, in sidebar for ex. and dofollow, you would most probably got PR6 on your own page you linked to.
I hope it clears things for you.
