An Certified Ethical Hacker is a  computer expert, who specializes in networking and penetration testing. This generally entails the following skill set –
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Expertise in various operating systems, primarily Linux and its various distribution. This is because a good portion of vulnerability testing includes invading the target system and sifting through their system. This is impossible without a good grasp on operating systems.
 
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In-depth knowledge of networking is also key to a successful ethical hacking career. This involves packet tracking, packet sniffing, intrusion detection & prevention, scanning subnets etc.
 
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Programming: Now programming is a vast topic with nuances in every language. As an ethical hacker, it is not expected of you to be a master-coder, but rather be a jack-of-all-trades.
 
Below is a table of the major/commonly used programming languages. Knowing these will definitely help you as an ethical hacker:
| Language  | 
Description | 
Reason to learn | 
| HTML | 
Used for creating web pages | 
HTML forms are used to enter data all over the internet. Being able to construct your own forms for analyzing vulnerabilities helps to figure out security issues in the code | 
| Javascript | 
Client-side scripting language. Also used for writing backend services | 
JavaScript code is executed on the client browser. Knowledge of JS can be used to read saved cookies and perform cross-site scripting etc. | 
| SQL | 
Used for interacting with databases | 
Using SQL injection, to by-pass web application login algorithms that are weak, delete data from the database, etc. | 
| PHP/Ruby | 
Server-side scripting. | 
PHP is one of the most used web programming languages. It is used to process HTML forms and performs other custom tasks. You could write a custom application in PHP that modifies settings on a web server and makes the server vulnerable to attacks. | 
| Bash | 
Creating small batch files and handy scripts | 
They come in handy when you need to write your own shellcodes, exploits, rootkits or understanding and expanding on existing ones. | 
Source : https://www.edureka.co/blog/ethical-hacking-tutorial/#Skills
Hope this helps!