$q = $modx->newQuery('modUser');

$q->innerJoin('modUserProfile', 'Profile');

$q->where(array(

    'Profile.city' => "Москва",

));

$q->select(array(

    "Profile.*",

    "modUser.*",

));

$s = $q->prepare();

$s->execute();

while($row = $s->fetch(PDO::FETCH_ASSOC)){

    print "". $row['username'];

}