This is a great question, and there is a building pile of learning SDN courses out there.
Perhaps the most technical one we found, we loved, and thanks to the great folks at Georgia Tech, the lectures were placed in the public domain. We assembled those video lectures and added our own quizzes and labs that aren't quite so computer science oriented, and more network science oriented at the Online School.
If you are looking for a higher level overview, either as a manager or as a starting point, we have an Overview/Briefing course here. This one is not free :-( (well we have to make the house payment somehow!)
The great news is that you can virtualize the network and study SDN on your own Windows or MAC laptop! So self study and expanding your knowledge of SDN could not be any simpler. To learn how to install the 'mininet' emulator for SDN, click here, it is free an easy.
We hope this helps you get in gear with SDN!