Where is the port to charge AC system located on a 1998 Chevy Malibu?

There isn't a port to charge the AC system on a 1998 Chevy Malibu (or any car) in the way you might be thinking of, like a phone charger. The AC system is charged using specialized equipment by a qualified technician. There are service ports (usually low and high pressure) on the AC lines, but these are not intended for DIY charging and require specialized gauges and refrigerants to add or remove refrigerant.