If you want the entire dataset duplicated, in order, you would repeat the set
statement.
data want;
do _iter = 1 to 4;
do _n_ = 1 to nobs_c;
set sashelp.class nobs=nobs_c point=_n_;
output;
end;
end;
stop;
run;
Of course, you could also just do
data want;
set sashelp.class;
do _n_ = 1 to 4;
output;
end;
run;
and then just sort the dataset by whatever is appropriate.