Sir i want to know birthday or date for my grandfather which is unknown it is possible by any of the method?

Not medically: Best bet is to check home records for documentation; then county/region of his birth, as usually recorded at varied levels. Can back-check older documents, like an ID/passport/school record--which should have birthday documented. If find same date 2+ times, have your likely answer.

No: however research can give you an approximate time if no records exist

No: There is no medical testing available to determine the exact date of ones birth. This type of information is often acquired by thorough investigative research of documents, possible old hospital reports, and eye witness accounts of people who may have known your grandfather, etc. and taking all that information into account, may be able to get you a date, or at least a guess of when he was born.

No medical means of: determining birth date. You need to investigate legal documents, If he has a social security # then he had to have provided a birth certificate. Check for a birth certificate in the city or town where he was born.