the original white pc engine don't have any Audio Video connection except for RF. you can buy an AV booster that slots into the back that gives you the composite RCA connections or a later model that adds battery back up RAM.
Or you can mod the console for either s-vid, RGB or even mod the AV booster
The later models of the pc engine ie coregrafx, coregrafx-II, shuttle and supergrafx have AV connections to composite RCA.