I am not aware of a simple command. Below is an attempt using the Window() function. However the resulting list includes any kind of window, e.g. data tables, that the script generates. To get only reports one need to filter out other types of windows.
nb=nitems(Window()); //number of windows before running script
//Actual script
New window("test1",textbox("test1"));
New window("test2",textbox("test2"));
//End of script
na=nitems(Window()); //number of windows after running script
// Build list of new windows
reportlist={};
for(i=0, i<=na-nb-1,i++,
insertinto(reportlist, window(i)<<get window title);
);
Show(reportlist);