All of your code is wrong on many levels. Starting from code standards where class should start with uppercase letter, formatting the code, finishing to calling a non-existent method.
First of all, your
inquiry class does not have the desired
query() method. It seems you try to give us a code you have not written by yourself, to debug.
Second, your class is completely USELESS. Even though it does not have a custom wrapping query method, you still could use PDO's method for querying and execute a query. However, even you are assigning value of object of type PDO to your
protected $pdo you have absolutely NO ACCESS to this
$pdo outside the class i.e. from
auth class. You should write an accessor for
$pdo, so you can use something like