My friend was 28 cycle day then she have a period on 16 of january she got unprotected sex during 28 of jan it is possible that she got pregnant...

Possible: If her period is regular she will likely ovulate around the 30th. She had unprotected sex on the 28. The sperm deposited during that day can survive upto 3 days. Hence it is possible.

Yes: It is possible, this was close to mid cycle. Always important to use contraception if pregnancy is not an option. Good luck!

Could be: The time she had unprotected sex was around when she may be ovulating, so this scenario would be a time when she could be fertile.