The Document Object Model (DOM) is the data representation of the objects that comprise the structure and content of a document on the web. This is what we use when we work with Javascript and interact in any way dynamically with the document.
If you use Angular, Vue, React, or any other library or framework to create modern web applications, the DOM is what these use under the hood.
If you want to stand out as a JavaScript developer, you need to learn DOM fundamentals.
You should have a basic understanding of Javascript and HTML.