What software should I install for NXT on OSX El 10.11.2 Capitan?
You can try installing the NXT 2.0 software. (See this question)

Here is a working link for the software: http://service.lego.com/en-us/HelpTopics/default.aspx?questionID=2655. Look for "How can I get a replacement for the LEGO® MINDSTORMS® NXT software for set 8547?"

It says that it will not install on OS X 10.10, however, I did successfully install it on 10.10 anyway. I have not tried installing it or running it on OS X 10.11 though.

There are open source alternatives, but the ones I have seen haven't been updated for a long time, so they may have problems running on newer versions of OS X as well.