The US Supreme Court doesn't use a standard court reporter, as trial courts do. The position most analogous is the Reporter of Decisions, who is responsible for ensuring oral arguments are recorded...
"To become a court reporter, you will need to go to school and become certified. There are many court reporter online colleges where you can get your certification."
At least 2 years, but for some people it can take up to 4. I got it from this website, which answers many other questions about court reporting. http://carrit.alfredstate.edu/infostart/faq.htm