my extended apple keyboard is not working after the el capitan upgrade
I upgraded to el capitan yesterday and my external apple keyboard stopped working
MacBook Pro with Retina display, 10.11
I had a similar issue after the el capitan upgrade. Eventually I solved the issue by going into system preferences and opening keyboard preferences.
First off, on the keyboard text tab, it told me that it did not recognise my keyboard. I hit the trial option, pressing the key immediately to the right of the left hand-side shift key. This identified the keyboard as a western europe ISO keyboard. I then went to the input source tab, and found that my keyboard type had been altered to U.S. (I have a British keyboard) I hit the + key at the bottom left and selected "British" from the drop down menu to admit to the list of option on my machine. I then selected "British" in the options. This solved all of my problems.
MacBook Pro 2014, El Capitan 10.1.1