I don't use dokan plugin. Here is the way to get the (post) author ID and to make your code work:
add_action( 'woocommerce_single_product_summary', 'display_author_name', 20 );
function display_author_name() {
// Get the author ID (the vendor ID)
$vendor_id = get_post_field( 'post_author', get_the_id() );
// Get the WP_User object (the vendor) from author ID
$vendor = new WP_User($vendor_id);
$store_info = dokan_get_store_info( $vendor_id ); // Get the store data
$store_name = $store_info['store_name']; // Get the store name
$store_url = dokan_get_store_url( $vendor_id ); // Get the store URL
$vendor_name = $vendor->display_name; // Get the vendor name
$address = $vendor->billing_address_1; // Get the vendor address
$postcode = $vendor->billing_postcode; // Get the vendor postcode
$city = $vendor->billing_city; // Get the vendor city
$state = $vendor->billing_state; // Get the vendor state
$country = $vendor->billing_country; // Get the vendor country
// Display the seller name linked to the store
printf( '<b>Seller Name:</b> <a href="%s">%s</a>', $store_url, $store_name );
}
Code goes in function.php file of your active child theme (or active theme). This should work now.
But I don't know how to get vendor rating and location. You should better ask Dokan support.
The code is based on this related thread.