<?php

$json = <<<JSON
{
	"@context": "http://s...content-available-to-author-only...a.org",
	"@type": "QAPage",
	"mainEntity": {
		"@type": "Question",
"name":"Кто такой \"срочник\" и что значит 
служба по 
контракту?","text":"", "author": {
			"@type": "Person",
			"name": "No Book"
		},
		"dateCreated": "2019-12-06T01:01Z+03:00",
		"answerCount": 1,
		"upvoteCount": 0,
"suggestedAnswer": [{
				"@type": "Answer",
				"text": "Деньги 
платят",
				"author": {
					"@type": "Person",
					"name": "Болтун  Первомайский"
				},
		"dateCreated": "2019-12-06T01:02Z+03:00",
				"upvoteCount": 0,
				"url": "https://w...content-available-to-author-only...l.ru/answer/1955965467"
				}]}}
JSON;

$json = preg_replace_callback(
	'/"[^"]*(?:""[^"]*)*"/',
	function($m) { return str_replace("\n", "\\n", $m[0]); },
	$json
);
print_r(json_decode($json));