As per Jekyll's doc, pagination for collections is not supported. I've tried to mimic Jekyll posts folder structure for my portfolio collection and then apply a slightly modified pagination Liquid syntax to work with a portfolio collection with no avail.
Is there a way/workaround in order to set up pagination for Collections in a Jekyll site?
jekyll-paginate only paginate posts.
If you want to paginate collections, you can use Octopress Paginate but it's not supported by github (for now).