First look at the platform, I am assuming you are going to work on application which are going to work on browser.

JS and related framework (Angular, React etc) are really important and must have for job.

Now come to back-end, big enterprises use .NET as a back-end but most of the startup or tech focus companies are using open source.

Now within open source there are multiple options like Java, Python, Ruby. I would recommend python as its very easy to start and great choice for many different kind of applications like web, data science/ML/AI.