Hello!
I had similar questions myself when I started learning programming. The choice of programming language depends largely on what you want to do as aside job. I guess of one of the easiest and fastest options will be to become front-end developer because you can find freelance projects easily and you need to know only HTML, CSS, JavaScript.
But I would recommend you to watch several videos on Youtube about different programming languages.
Many people recommend Python as it's quite logical and can be used in different spheres. You can then you it for data analysis apart from 'programming'
You won't know unless you try