Site title not showing. Please help me

Use this code in Header.php file.

<title><?php wp_title(' - ', true, 'right'); ?></title>

But as per page view source code.you have forgot to close tag above tag in header. so please close tag. see this screenshot

Should code like this:

<script>
window.dataLayer = window.dataLayer || [];
function gtag(){dataLayer.push(arguments);}
gtag('js', new Date());
</script>
<title><?php wp_title(' - ', true, 'right'); ?></title>