This one’s easy. In order to review individual test sends along with the winning subject line you need to go to 'Sent Messages' while in the Console.
From the Home Page, on the left hand navigation bar select Send > Email > Sent Messages.
This will display the following page:
From here you can filter the results by number of recipients or date. In the case of a split test the best way to find the send you are looking for is to filter by date. This will then display the split tests and the winning subject line.
The easiest way to locate your split test by is by looking at the recipient column where there will be 3 (or more depending on your split test) rows with the exact same amount of recipients. Usually the winning subject line will be displayed directly above the split test.
On some occasions, other emails may have been sent out in between the spit test and the sending of the final winning subject line. The longer the specified period between the winning subject and the split tests, the bigger the chance of this occurring.