You must know a programming language from Java, Python, JavaScript, C#, PHP, Ruby. After that, you must know the basics of HTML like how HTML elements work and their different operations. And you also know how to work with the database not in-depth but at least some basics should be clear. You can easily get this skill to become a Selenium developer by enrolling yourself in the following Selenium Training Course. Also, watch the following Selenium video tutorial to learn more about it.