Submission of fake certificates in order to get a job in the government or in any private sector is a punishable offence and the person doing so can be punished and also be terminated from the job that he is currently posted to. Whoever commits forgery shall be punished with imprisonment of either description for a term which may extend to two years, or with fine, or with both. Imprisonment for 2 years, or fine, or both.
Now, you are alleging that a person used faka certificates in order to get the job. Now, you need to prove this. You must collect evidence in order to prove your proint. This can be in the form of audio clips, eye witnesses and so on. You need good proof of the same. Without proof, you will not be able to prove your point. If the job which he got was a government job then the punishment is more severe.
Before filing the case against him, you advise you to confront about the false caste certificates. You can record this conversation. It will help you. Also once you collect the evidence, you can show it to the higher authorities of the company or the department in which he is working and can get his job terminated.
Reference: Section 464 of the Indian Penal Code,1860