Nevada recently published a Commerce Tax Registration Process Informational Chart. It is a flow-chart that can help your corporation determine if they need to register.
If your corporation is organized or incorporated in Nevada, it will be registered automatically. All other corporations should make the determination based on answering a nexus questionnaire.
At the end of March, beginning of April, corporations will receive a "Welcome to Commerce Tax" letter (how nice). The letter will have your corporation's Tax ID number on it. Go to the chart for additional details.
Also, check out Nevada's website or my previous posts on the Nevada Commerce Tax.