As this information is not available on the public facing Partner pages I must assume that Juniper does not wish to disclose this to companies that have not begun the application process. They have three levels, reseller, select and elite. I would assume that just about any capable reseller can become a Juniper reseller and once you have done so you would learn the requirements of the other levels. Or you could begin the application process and I am sure you will learn more.
I will say as an Elite reseller that we have to have multiple sales people and engineers that must maintain a pretty high level of CEC's (continuing education credits) each year to stay at the Elite level. These are offered up through the Juniper Partner site.
Furthermore to become an Elite we had to have multiple engineers pass JNCIA, JNCIS tests in the areas that we wish to sell. I don't feel comfortable going beyond that desciption.