If you want to test web applications, it is good to know what information you can get from
the Dev Tools browser. To complete your bug report, you need to be able to analyze HTTP requests and responses, read the console and have a basic understanding of HTML5 / CSS3
If you want to test mobile applications, it is worth keeping up with the latest iOS / Android system versions, knowing how to read phone logs and having an idea of how Android Studio and Xcode work.
Xcode: available on macOS
A tester often has to test using different environments. How? It is worth knowing how to create a Virtual Machine to facilitate your work.
Do you know how to use a terminal? Do you know basic commands such as mkdir, ls, or cd? If so, great! If you haven’t heard of this, learn about command lines. If the project hasn’t been uploaded to the test environment yet, you can always test it locally.
Knowledge of command lines will be needed.
The ability to use Git is a handy skill. At the beginning of your career, you should know some basic commands, such as git clone.
You should understand the basics of relational and non-relational databases and know what the difference between them is.