You can find your REST API keys and JavaScript snippet keys in the Console here, or by following these instructions. 

1. Once signed into the console, click the "Developer" link in the left side menu:

2. In the next screen, click on "API keys" in the menu on the center of the page:

You will now see a page listing your Production or Sandbox keys, depending on which account you are viewing:

You also have the ability rotate or swap your API keys on this page. Find out the differences between your sandbox and production accounts here.