Do you work with the react native should learn react.js?

That would depend on what you would like to do. Both are open sourced by Facebook:

ReactJS: This is basically a JavaScript library used mainly as the V in MVC. But it can also render on the server side using Node. It can power user interfaces, web applications and native apps using React Native.

React Native: This is a mobile framework that enables you to build native mobile applications using a consistent developer experience based on JavaScript and React.

Yes, it is advised to learn React before you start with React Native, since the principles you'll need when developing in React Native are all based on React.

From Facebook:

React Native enables you to build world-class application experiences on native platforms using a consistent developer experience based on JavaScript and React.

So before you study all the mobile specific API's and attention points, it's good to be familiar with React itself.