How can I write custom query in Magento 2 format

With ObjectManager

$objectManager = \Magento\Framework\App\ObjectManager::getInstance(); // Instance of object manager
$resource = $objectManager->get('Magento\Framework\App\ResourceConnection');
$connection = $resource->getConnection();
$tableName = $resource->getTableName('your_table_name'); //gives table name with prefix

$sql = "SELECT * FROM ( SELECT * FROM ".$tableName." WHERE customer_id IN ( 0, 5 ) ORDER BY feed_id DESC ) AS t1 GROUP BY position limit 0,5";
$result = $connection->fetchAll($sql);

With Factory Method

<?php

protected $_resourceConnection;

public function __construct(
    ...
    \Magento\Framework\App\ResourceConnection $resourceConnection,
    ...
) {
    ...
    $this->_resourceConnection = $resourceConnection;
    ...
}

public function getTableName()
{
    return $this->_resourceConnection->getTableName('your_table_name');
}

public function getCollection()
{
    $tablename = $this->getTableName();
    $connection = $this->_resourceConnection->getConnection();
    $query = "SELECT * FROM ( SELECT * FROM ".$tablename." WHERE customer_id IN ( 0, 5 ) ORDER BY feed_id DESC ) AS t1 GROUP BY position limit 0,5";  
    $result = $connection->fetchAll($query);

    return $result;
}