create table t1 (col1 varchar2(10), col2 varchar2(10));
insert into t1 values ('FirstCol', 'SecondCol');

CREATE OR REPLACE PACKAGE ref_cur_tst
IS
   -- weak ref cursor
   TYPE t_cur IS REF CURSOR; 

   PROCEDURE get_t1 (cv_cur IN OUT t_cur, p_col IN varchar2);
END;
/
CREATE OR REPLACE PACKAGE BODY ref_cur_tst
AS
   PROCEDURE get_t1 (cv_cur IN OUT t_cur, p_col IN varchar2)
   IS
   BEGIN
      OPEN cv_cur FOR 'SELECT '||p_col||' FROM t1';
   END;
END;
/


DECLARE
   a       varchar2(10);
   cv_c1   ref_cur_tst.t_cur;
   p_col  varchar2(20) := 'COL1';
BEGIN
   ref_cur_tst.get_t1 (cv_c1, p_col);

   LOOP
      FETCH cv_c1 INTO a;
      EXIT WHEN cv_c1%NOTFOUND;
      DBMS_OUTPUT.put_line (a);
   END LOOP;
   CLOSE cv_c1;
END;
/