What exactly do you mean by "the IOS of a device"?
If [ PatternCount ( Get ( ApplicationVersion ) ; "Go_iPad" ) ]
would detect that an iPad has opened the file.
If [ PatternCount ( Get ( ApplicationVersion ) ; "Go" ) ]
would detect that an iOS device has opened the file.
You can look up Get ( ApplicationVersion ) in FileMaker Help to learn more about this function.
Sorry, that is what I mean. If I'm accessing files remotely through FM Go I want it to automatically select a specific layout optimised for iphone or ipad.