you can search it in page sources for term "rel=nofollow" otherwise there are lots of seo tool on the internet which are providing this facility. i am using SearchStatus 1.33 add-on to identify do-follow and no-follow links.
You can view the webpage's source and from there you can check if a link has a nofollow or dofollow tag. Here's an example on how they look. 1. No Follow links - <a rel="nofollow" href="http://www.domainname.com">Domain Name</a> (i just made it bold to add emphasis ) 2. Do Follow links - <a href="http://www.domainname.com">Domain Name</a> As you have noticed, do follow links don't need tags like the nofollow tag as they are always do follow by default unless you add the nofollow tag to make it no follow.
For checking it, use nodofollow pug-in for firefox. You can know whether the link you make is nofollow or not. look at commenthunt.com, or look in http://followlist.com/ They will provide some website that not give "nofollow" tag. You can also search in google for dofollow directory
If you are using Firefox there is one addons which I use, named "searchstatus". It is a great tool for SEO purpose and help us to check either the link is dofollow or nofollow. The other option is to check in source code.