If you want to synchronize a light show, sequencer, or visuals with the beat grid established by Pioneer nexus club gear (using their DJ Link protocol), I have just released an open-source Java library which makes that very easy. You can find beat-link on GitHub, along with extensive introductory and API documentation.

If you want to port this capability to a non-JVM language, in addition to simply examining  the Java source of beat-link, you can also use my research tool and detailed analysis document (which were what enabled me to build beat-link). Also found on GitHub, dysentery is written in Clojure, but you can run it as an executable Jar without worrying about that if you just want to use it to study what your Pioneer gear is up to.

If you have any nexus gear other than the DJM-2000 and CDJ-2000, I would very much appreciate learning how that differs from what I have seen so far, so I can update the analysis document and (if necessary) beat-link itself. Also, if you can help figure out any of the as-yet unexplained portions of the protocol, that would be delightful! Please open issues or contact me by email.