WordPress function::: get_header();

No, because get_header() calls locate_template() with load_once = true, meaning the actual template PHP is included with require_once

    if ( $load_once ) {
        require_once $_template_file;
    } else {
        require $_template_file;
    }

so the second time you call it it won’t load anything, as it’s already loaded the same file before.

This makes sense for header because typically header includes the the html, head and body tags to set up the page – you wouldn’t want to include it twice. Documentation here.

(If you meant is it safe to accidentally call get_header() twice then yes it is, the second call won’t do anything. But you shouldn’t be calling it twice no.)

If you have a separate block that you do want to include twice you can use get_template_part().