It depends what you currently know, the scale of th apps you want to build and how professionally you want to make them.
Those are the minimum…
Additionally, you may want to look at front end libraries or frameworks, such as Angular, React, Ember, Backbone, Vue, Bootstrap.
You will also need to understand how npm modules work and will likely incorporate many of these into your Node backend.
You may also want to look at task runners such as Gulp or Grunt (or simply rely on npm scripts).
Then there is testing, which is not strictly necessary for your own personal projects, but if you are working for someone who knows what they are doing, then picking up various testing frameworks would also be beneficial: Mocha, Chai, Sinion, Karma, Selenium…