In my company some employee has served the notice period of 30 days , 15 days and also for 60 days and some has not served also. Now I am confused

There is nothing like a general notice period. Mostly for entry to middle level it is 30 days and it can be 3 months for senior level depending upon the current status of projects and position they are handling. Again it is depending on companies policy.
You can refer your appointment letter to know your notice period.