How to get order item collection by item id magento 2?

You can get item collection data by Item id in Magento 2 by using below code snippet, Create Block file,

<?php
namespace Rbj\Training\Block;

class Item extends \Magento\Framework\View\Element\Template
{
    public function __construct(
        \Magento\Framework\View\Element\Template $context,
        \Magento\Sales\Api\OrderItemRepositoryInterface $orderItemRepository,
        array $data = []
    ) {
        $this->orderItemRepository = $orderItemRepository;
        parent::__construct($context, $data);
    }

    /* get order Item collection */
    public function getOrderItem($itemIid)
    {
        $itemCollection = $this->orderItemRepository->get($itemId);
        return $itemCollection;
    }
}

Call function from the Template file,

$itemId = 10; // order item id
$getItemCollection = $block->getOrderItem($itemId);
echo $getItemCollection->getOrderId();
echo "<pre>";print_r($getItemCollection->debug());