functions.php

<?php

function gg_asset_url( $path = '' ) {
  return esc_url( get_template_directory_uri() . '/assets/' . $path );
}

function gg_asset_path( $path = '' ) {
  return get_template_directory() . '/assets/' . $path;
}

function gg_assets() {

  wp_enqueue_style(
    'gg-style', // name
    gg_asset_url( 'css/style.css' ), // file URL
    array(), // dependencies
    filemtime( gg_asset_path( 'css/style.css' ) ) // `ver` paramater value
  );

  wp_enqueue_script(
    'gg-script', // name
    gg_asset_url( 'js/script.js' ), // file URL
    array( 'jquery' ), // dependencies
    filemtime( gg_asset_path( 'js/script.js' ) ), // `ver` paramater value
  );

}
add_action( 'wp_enqueue_scripts', 'gg_assets' );

query-string-modified.php

<link rel="stylesheet" href="my/css/file.css?ver=<?php echo filemtime(__DIR__ . '/my/css/file.css'); ?>">
<script src="my/js/file.js?ver=<?php echo filemtime(__DIR__ . '/my/js/file.js'); ?>"></script>

query-string-timestamp.php

<link rel="stylesheet" href="my/css/file.css?ver=<?php echo time(); ?>">
<script src="my/js/file.js?ver=<?php echo time(); ?>"></script>

query-string.php

<link rel="stylesheet" href="my/css/file.css?ver=1">
<script src="my/js/file.js?ver=1"></script>