You can either look at the source code which is time consuming or I recommend downloading this tool bar http://tools.seobook.com/firefox/seo-for-firefox.html Its free and it shows all the links on any page whether they are do-follow.. Watch the video on the link and you'll get an idea how it all works, plus it has alot of other good things. Good luck
I'm using firefox add-on (SearchStatus) to check the dofollow or nofollow. It is very easy to use. Wish this can help you
You could do with using the search button on this forum to find the answer. But as I'm here: Press ctrl+u to get the source code up and then press ctrl+f to search for the word "nofollow". If links (such as in comments) have rel=nofollow then you will know that your link will be nofollow. But if there are no comments on the blog, then you won't know if links are nofollow or dofollow until you have posted a link yourself.
Those plugins that they mention don't properly render rel="external nofollow" properly..... Read this blog post for a simple firefox solution that is great for showing nofollow: How to easily spot nofollow links...
I use searchstatus to show all of the no-followed links on blogs. Very useful other tools included as well.