How to print array of specific item

Not really a WordPress question, but I’ll bite.

That data is JSON. To manipulate it with PHP you need to decode it with json_decode(). Then you can treat it as a PHP object.

So to access the values you’d mention, and assuming the JSON is in a variable named $json:

$object = json_decode( $json );
$staff_name = $object->items[0]->staff_name;
$coupon = $object->coupon;