// Get an instance of the WC_Order object
$order = wc_get_order($order_id);

// Iterating through each WC_Order_Item_Product objects
foreach ($order->get_items() as $item_key => $item ):

    ## Using WC_Order_Item methods ##

    // Item ID is directly accessible from the $item_key in the foreach loop or
    $item_id = $item->get_id();

    ## Using WC_Order_Item_Product methods ##

    $product      = $item->get_product(); // Get the WC_Product object

    $product_id   = $item->get_product_id(); // the Product id
    $variation_id = $item->get_variation_id(); // the Variation id

    $item_type    = $item->get_type(); // Type of the order item ("line_item")

    $item_name    = $item->get_name(); // Name of the product
    $quantity     = $item->get_quantity();  
    $tax_class    = $item->get_tax_class();
    $line_subtotal     = $item->get_subtotal(); // Line subtotal (non discounted)
    $line_subtotal_tax = $item->get_subtotal_tax(); // Line subtotal tax (non discounted)
    $line_total        = $item->get_total(); // Line total (discounted)
    $line_total_tax    = $item->get_total_tax(); // Line total tax (discounted)

    ## Access Order Items data properties (in an array of values) ##
    $item_data    = $item->get_data();

    $product_name = $item_data['name'];
    $product_id   = $item_data['product_id'];
    $variation_id = $item_data['variation_id'];
    $quantity     = $item_data['quantity'];
    $tax_class    = $item_data['tax_class'];
    $line_subtotal     = $item_data['subtotal'];
    $line_subtotal_tax = $item_data['subtotal_tax'];
    $line_total        = $item_data['total'];
    $line_total_tax    = $item_data['total_tax'];

    // Get data from The WC_product object using methods (examples)
    $product        = $item->get_product(); // Get the WC_Product object

    $product_type   = $product->get_type();
    $product_sku    = $product->get_sku();
    $product_price  = $product->get_price();
    $stock_quantity = $product->get_stock_quantity();

endforeach;