Reputation is the karma given to you.
That section you found under your User CP, called "Latest Reputation Received" is the area that shows:
Thread (and post that you were given karma) Date (the date you were given karma) Posted By (who gave you the karma) Comment (sometimes there will be a comment here from the karma giver to you)
The column "Thread" will have the thread name, which is a link that you can click to see which post of yours was given karma.
The column "Posted By" will have a link to the karma giver's profile page so you may thank them for the karma.