I think Hunter Biden was involved with China, too. Or maybe it was Joe directly...but in any case there was a reason for Trumps question.
China gave him a billion and a half dollars or so. According to the Washington Times One of the companies in the 2015 deal was Bohai Harvest RST (BHR), a billion-dollar investment fund backed by China that was formed by Hunter Biden and Chris Heinz, the stepson of then-Secretary of State John Kerry.
If you look up BHR, it's basically China stuffing a company full of money to investments overseas including hostile investments.