It'll be the braided shield and the thickest red cable, but:
You'll be a bit disappointed in the current you'll be able to draw.
The USB-C specification allows for chargers to deliver high currents, but only to devices that speak the USB-PD profile. That's a complex protocol, and just cutting off the wires will not do it. See this answer that discusses what you'd need to do to convince a USB-C charger to deliver 20 V.
By the USB standard, your charger mustn't deliver more than a couple hundred milliamperes to a "dumb" device that doesn't negotiate a higher current; most chargers will deliver solidly more, but you won't be close to the maximum charging current, if you don't talk USB PD to the charger.
In older USB2 devices, Qualcomm QC is the most popular protocol to negotiate a high current draw; basically the same applies for QC as for USB PD.