template_redirect

add_action( 'template_redirect', 'wpdocs_require_login_for_books' );

function wpdocs_require_login_for_books() {
	if ( is_singular( 'book' ) && ! is_user_logged_in() ) {
		wp_safe_redirect( wp_login_url( get_permalink() ) );
		exit;
	}
}

This action hook executes just before WordPress determines which template page to load. It is a good hook to use if you need to do a redirect with full knowledge of the content that has been queried. Note: Loading a different template is not a good use of this hook. If you include another template and then use exit() or die(), no subsequent template_redirect hooks will be run, which could break the site’s functionality. Instead, use the {@see 'template_include'} filter hook to return the path to the new template you want to use. This will allow an alternative template to be used without interfering with the WordPress loading process.

// rejestracja funkcji zwrotnej
add_action( 'template_redirect', 'twoja_funkcja' );

function twoja_funkcja($param_1) {
	// Twój kod
}