How can get all users by current user meta?

You can achieve this using get_users function and its meta_key argument as displayed below.

$users = get_users(array(
    'meta_key'     => 'blocking_users',
));

var_dump( $users );

To retrieve it for current user and print it, please use below code.

$user_id = get_current_user_id();
$key = 'blocking_users';
$single = false;
$blocking_users = get_user_meta( $user_id, $key, $single ); 
echo '<p>The '. $key . ' value for user id ' . $user_id . ' is: </p>'; 
print_r($blocking_users);