Node.js is a runtime environment that lets developers use JavaScript to write server-side scripts or back-end services. It is an open-source, cross-platform technology that is designed to create scalable network applications by executing JavaScript codes outside the browser. By featuring an event-driven, non-blocking I/O model, Node.js allows for the development of lightweight and efficient applications, making it an increasingly popular choice for developers.

With Node.js, developers can create real-time applications like chats and gaming apps, APIs and data streaming applications. It is also used for creating simple websites and backend systems that have the ability to process large amounts of data securely and efficiently.

Certain job roles, including but not limited to, back-end developers, full-stack developers and software engineers, may require Node.js in their tech skill set. It is highly sought after in the tech industry due to its ability to improve speed and productivity, and companies are continuously looking for candidates with Node.js skills.

Candidates eyeing various job roles requiring Node.js might find it beneficial to lay a strong foundation in JavaScript since Node.js is built on JavaScript engine. Understanding JavaScript not only makes learning Node.js much easier, but it also ensures that developers are equipped with the fundamental coding skills required by Node.js.

Beyond JavaScript, candidates should also possess knowledge in understanding server-side development and API's. It would be advantageous to have experience in other JavaScript libraries and frameworks like AngularJS, ReactJS or Vue.js. Familiarity with database technology such as MongoDB or Express.js, which are often used in conjunction with Node.js, can also be a significant advantage.

In summary, mastering Node.js requires a deep understanding of JavaScript, foundational knowledge of server-side development and familiarity with other related technologies. With this skill, candidates can effectively add value to companies by being efficient and resourceful in building high-speed, scalable network applications.