How to get list of env variables from the root folder to jenkins job? Using configure option, when we check the environment variables, we
  get only the variables which are available with in the folder or job.
  But, I want to get complete list of env variable from the root folder
  to the folder/job, which I want to see.
I recommend that you use the printenv command for list system Variable:

printenv


and also An easy way to obtain the Jenkins environment variables list from your local installation is to append env-vars.html to the server's URL. the URL would be 

http://{jenkins_url}/env-vars.html