Add a login/logout link to the menu bar of any Genesis child theme

functions.php

<?php // add everything except for this opening line to your functions file

add_filter( 'wp_nav_menu_items', 'sp_add_loginout_link', 10, 2 );

function sp_add_loginout_link( $items, $args ) {
	// Change 'primary' to 'secondary' to put the login link in your secondary nav bar.
	if ( $args->theme_location != 'primary' ) {
		return $items;
	}
	
	if ( is_user_logged_in() ) {
		$items .= '<li class="menu-item"><a href="' . wp_logout_url( home_url() ) . '">Log Out</a></li>';
	} else {
		$items .= '<li class="menu-item"><a href="' . site_url( 'wp-login.php' ) . '">Log In</a></li>';
	}

	return $items;
}

Here's another way to do it wp_loginout https://codex.wordpress.org/Function_Reference/wp_loginout