There are at least two formulations of the learning paradox in the dialogue called Meno, by the philosopher Plato. In that dialogue the character Meno suggests that it is futile to try to learn anything. If you don't know what the thing is you can't learn it, becuase you don't know what it is you are looking for, and wouldn't recognize it if you found it. And if you do know what the thing is you can't learn it, because you already know it, and learning is for things that are unknown.
The paradox has a number of formulations. The Meno is very short. I suggest you read it for yourself.
As a PR newbie, I find the learning paradox most relevant to the central point as stated by Paul: the importance of stating a purpose. As Paul mentions in the tapes, it is difficult to know your purpose for reading something, when you don't know anything about that thing which you are reading. If I don't know what a book is about, how can I know what I want to get from that book?
Socrates' apparent solution is rather unsatisfactory. He assumes we learned in an earlier reincarnation. But why wouldn't the learning paradox prevent us from learning in previous lives if it prevents us from learning in this life?
The deeper socratic solution is that we have innate knowledge. An example would be the Chomskyan notion that we are all equipped to learn natural languages with little effort, since those languages are congruent with our brain's structure. Chomsky points out that children exposed to very limited environments still learn the same language as children in very enriched environments. Language learning seems to be something we are programmed to do. It's innate.
The PR solution to the learning paradox is based on a distinction between knowing a thing by being acquainted with it and knowing a thing by knowing some of its properties. There are many people who know about the jewish bible, but have never read it. They know about Noah and the flood, but have never read the bible's account.
You can know about a book and establish a purpose before you have read the book and have become acquainted with it. As Paul points out, as you acquaint yourself with a book (article, etc.) you might adjust your purpose.