Actually, first you need to clarify your terms -- what do the terms "mainframe simulator" and "mainframe real time environment" mean to you? "Real time" processing has a very specific meaning in IT, and mainframes are practically never involved in real time processing -- so there is a very good chance you are using the term incorrectly to mean something that it does not mean to IT professionals.
If you are asking how to tell if you are running on a simulated mainframe or actual mainframe, the only real way to know is to ask the systems support group that supports the system since the whole point of a simulator is to replicate the mainframe. However, since the use of simulators is almost exclusively limited to hardware manufacturers, unless you're working with one of those very few companies the answer almost certainly will not be that you're running on a simulator. You might be running on an emulator (such as Hercules) or an actual z/archictecture machine -- but again the only way to know for sure is to ask whoever supports the system.