Hey there! Yes, Hadoop is a trending technology with lots of job opportunities.
You dont need to know anything in particular before learning Hadoop. Hadoop is just a tool for Big Data. So, if you are learning Hadoop then you will learn everything you need in that process.
But knowing some things would be advantageous for you, such as:
- Basic knowledge of program languages such as Java, nodejs
- Basic knowledge of query language such as MySql
- Basic knowledge of *nix OS.