At conference in korea, do i need transit visa to visit my daughter in china for 2 days and how?

Chris, yes, you need it to visit your daughter in PRC. You can try to apply for a tourist L type from Korea. The first thing is to prepare the required documents including your passport and copy of its data page, the completed application form affixed with a passport-style photo, your valid entry permit to Korea, and an invitation letter from your daughter. And then submit your application to the CVASC to apply for it.