You need to find out which networks are available, and then pass them into CNCopyCurrentNetworkInfo. For example:
CFArrayRef myArray = CNCopySupportedInterfaces();
CFDictionaryRef myDict = CNCopyCurrentNetworkInfo(CFArrayGetValueAtIndex(myArray, 0));
…and you can then use the kCNNetworkInfoKeySSID on the dictionary you’ve got back (myDict) to find out the SSID. Don’t forget to release/manage memory appropriately.