It's a version of the old Nina Simone song, "I wish I knew how it would feel to be free." It was covered by the Lighthouse Family &, more recently, in the Coca Cola advert.
The version used on the show is by the Billy Taylor Trio. Billy Taylor is credited as the writer on his own version and also on the Lighthouse Family's cover, so I guess it is the original - not Nina Simone's version.