Kamdar can be a Jain surname, but it is not only a Jain surname.

• Many Gujarati Vaniya / business families with the surname Kamdar are Jain (both Śvetāmbara and Digambar in some regions).
• The same surname is also used by non‑Jains (Hindus, etc.).
• In Jainism, being Jain is about following Jain dharma and practices, not about a particular surname. A surname alone can never guarantee that someone is Jain.

So: Some Kamdar families are Jain, some are not. To know for sure, you have to see the person’s actual religious practice and family background, not just the last name.

For a simple explanation of how surnames and Jain identity work, you can read more here