What should I learn ????

Answer 1

Hello, Linh Pham !
Both C++ and java are object oriented languages. More java projects are coming up which makes it an advantage to know it. for Java is the best book to start with. But, as others have told, it will take time to master it. But as a freaher, only understanding of core concepts and a little bit of syntax will do. Once you have some confidence, do try to take up SCJP certification. Whether you take it or not, at least preparing for it will give you good insight on correct syntax and key words/reserved words.
https://www.sololearn.com/Course/Java/?ref=app
https://www.sololearn.com/Course/CPlusPlus/?ref=app

Answer 2

You can do both courses in a short time. Why not do them both. It will give you an idea what the differences are.

Answer 3

Java. C# is stupidly easy to learn if you know Java, and is actually pretty powerful for web automation and Windows development. Java is also powerful and more ubiquitous, used in more things, and runs on pretty much everything. Both are object oriented and easy to package. I've used both a lot and love both, just for different things. C# definitely has a big step up with GUI apps, but most companies etc. look for Java.

Read Here some benefits of learning java: http://crbtech.in/Java-Training/benefits-learning-java/