How to view SQL generated by Query Builder?

$sql= "SELECT COUNT(*) FROM business_components WHERE email= ? AND campaign= ? AND IUS= ?";
$query =$this->db->query($sql, [ $_SESSION['userid'],$_SESSION['campaign'],1]);
$res=$query->result();

This works except I don't know how to get the result

I tried this 'num_IUS' => $res[0]. The value in $res[0] is COUNT(*)="2". 2 is the correct answer but how do I get that into num_IUS?

proof that an old dog can learn new tricks