Which all jars do I need to register to use the elephant-bird-pig-JsonLoader function?
You need simple json as well.
REGISTER json-simple-1.1.1.jar
REGISTER elephant-bird-pig-4.10.jar
REGISTER elephant-bird-hadoop-compat-4.10.jar
REGISTER elephant-bird-core-4.10.jar
After this the following command will work
MY_JSON = LOAD 'myfile.json' USING com.twitter.elephantbird.pig.load.JsonLoader('-nestedLoad');