You need two flags when specifying which target to emulate. Also, do not include the version number on the end.
Find out what emulator images are available. Again, take into account that the version number will not be included when specifying the target in the cordova call.
./platforms/ios/cordova/lib/list-emulator-images
iPhone-5, 10.3
iPhone-5s, 10.3
iPhone-6, 10.3
iPhone-6-Plus, 10.3
iPhone-6s, 10.3
iPhone-6s-Plus, 10.3
iPhone-7, 10.3
iPhone-7-Plus, 10.3
iPhone-SE, 10.3
iPad-Air, 10.3
iPad-Air-2, 10.3
iPad-Pro--9-7-inch-, 10.3
iPad-Pro, 10.3
Apple-TV-1080p, tvOS 10.2
Apple-Watch-38mm, watchOS 3.2
Apple-Watch-42mm, watchOS 3.2
Apple-Watch-Series-2-38mm, watchOS 3.2
Apple-Watch-Series-2-42mm, watchOS 3.2
cordova run ios --emulator --target="iPad-Air"