Thank you for the reply. However I didn't manage to solve my issue yet.
After opening an existing .jrp file, which in turn opens a data table and a report window, the following scripts:
wList = Get Window List(Type("Reports"));
print(wList[1] << report << Get Scriptable Object() << get script());
wList = Get Window List(Type("Reports"));
print(wList[1] << Get Scriptable Object() << get script());
will both result in
HeadBox(V List Box(Box(OutlineBox(H List Box(NoCloneBox(IfBox(H List Box(V List Box(H List Box(ButtonBox, ButtonBox, ButtonBox), BorderBox(V List Box(H List Box(PopupBox, Text Box("40 Columns")), V List [... etc.]
Not the kind of script I am looking for. This seems to be a special case, since I'm starting with an existing report window. What am I doing wrong?