There is no documented way to get this information. What follows is therefor subject to change in future versions.
As with most objects in Mathematica, you can "look behind the curtain" by using FullForm:
In:
M // FullForm
Out:
WSMSimulationData["/tmp/WolframSystemModeler-malte/WSMLink/wsml_HelloWorld_lsim_247785_1.mat","IntroductoryExamples.HelloWorld",2,List[0.`,10.`],1,List[],List["x"]]
From this you can see that the first element is a path to where the result file is stored.
The simulation settings file (.sim) and simulation executable (.exe) information is not stored in the WSMSimulationData object, as they are not needed for anything you can do with such an object.