Electrical – What are the proper labels for these wires in this AC power cord

ALWAYS switch the live wire(s). If you only switch the neutral, then the entire circuit becomes live when switched off.

Switching the neutral also can add some safety in case the outlet is wired backwards. It would also allow you to give it 120-0-120 split phase later on (240v total), if it's rated for that.

Do NOT switch the ground, but you probably knew that.

In case you didn't know, neutral is actually the center tap of the utility transformer outside and is (supposed to be) connected to ground (dirt) in the breaker box and nowhere else. This is why it's okay to leave the neutral connected in most cases. However, don't be tempted to use ground to carry current just because it goes to the same place. Neutral is there because the current that it carries causes it to not be ground anymore once it leaves the breaker box.

Yes the power and ground lines are needed. The ground line is needed because the OTG feature works by grounding the ID pin the the USB plug. If the ID pin is left floating then the object configures as a device. If the pin is grounded then the object configures as a host. The power line is needed because most if not all devices use the presence of power as a trigger to initiate USB enumeration. If no power is present then the object will not check the data lines to see if something is present.