Err.. it doesn't really work that way. To learn how to look for vulnerabilities you need to learn how to read code(and learn how to code, obviously). It's not really a job where you read some guide and after a week you can start looking for vulnerabilities.
Right you need lot of experience in coding and debugging with development environment to find out the bugs in certain codes as it's not easy if you are not from technical background and why would anyone be hiring you without any prior experience?
There are lot of developers who have found bugs in some applications or code of companies and get paid for it but you need to have that mindset and knowledge for the same.
Like if he is interested he can try out something similar:
Bug bounty FortuneJack