The valueChangeListener is only necessary, if you are interested in both the old and the new value.
If you are only interested in the new value, the use of or is the better choice.
There are several possible reasons, why the ajax call won't work. First you should change the method signature of the handler method: drop the parameter. Then you can access your managed bean variable directly:
public void handleChange(){
System.out.println("here "+ getEmp().getEmployeeName());
}
At the time, the listener is called, the new value is already set. (Note that I implicitly assume that the el expression mymb.emp.employeeName is correctly backed by the corresponding getter/setter methods.)