Magento 2 get all attributes from the default products attribute set (id: 4)
<?php
/** @var $coll \Magento\Eav\Model\ResourceModel\Entity\Attribute\Collection */
$coll = $this->_objectManager->create(\Magento\Eav\Model\ResourceModel\Entity\Attribute\Collection::class);
// add filter by entity type to get product attributes only
// '4' is the default type ID for 'catalog_product' entity - see 'eav_entity_type' table)
// or skip the next line to get all attributes for all types of entities
$coll->addFieldToFilter(\Magento\Eav\Model\Entity\Attribute\Set::KEY_ENTITY_TYPE_ID, 4);
$attrAll = $coll->load()->getItems();