Wiring 16-pin USB-C jack to USB-to-UART controller
They should be connected together (A6 to B6 and A7 to B7). Actually you have only one differential pair D+/D-. Because USB-C plug is flippable, there are two connections for D+ (A6 and B6) and two connections for D- (A7 and B7) on a receptacle. This way D+ is always connected to D+ and D- to D-.

USB-C Receptacle 



Image source: USB-C on Wikipedia

USB-C Plug



Image source: USB-C on Wikipedia