- Programming fundamentals in JavaScript, C++ or Java, SQL, and Python or Ruby. Or a few languages very similar to that set.
- Data structures including trees, graphs, queues, stacks, heaps, sets, lists, arrays. Learn how all these work, how to use associated functions for each, and be able to code them from scratch on your own (you will never need to, but should know how to).
- Algorithms including list sorting, tree and graph traversal, minimum spanning tree, etc. and time and space complexity of algorithms.
- Object oriented design, classes, inheritance.
That’s most of what you need to know. And that’s what most job interviews focus on. Of course there’s much more to computer science. And if you want to specialize in anything then you need some additional skills.