Procedures In Oracle
You are only printing the last row, not every row:

You need to move the dbms_output inside the loop:

create or replace procedure Display
is
  cursor ABC is
    select empno, ename, sal
    from emp
    where deptno=10;

  emp_rec ABC%rowtype;

Begin
  Open ABC;
  Loop
    fetch ABC into emp_rec;
    exit when ABC%notfound;

    --- the output needs to be here
    dbms_output.put_line(emp_rec.empno||'   '||emp_rec.ename||'  '||emp_rec.sal); 
  end Loop;
end;
/