gistfile1.txt

  $innerdata = json_decode('{
            "sync_block": false,
            "nest_uid":"1_1_1536657342_lyBhkbkLYT"
            "contacts": [{
                "con_title": "",
                "con_fName": "",
                "con_lName": "",
                "con_job_title": "",
                "emails": [{
                    "email": "",
                    "type": "",
                    "primary": false,
                    "nest_uid": "1_1_1536657342_lyBhkbkDfG",
                    "checked": false
                },
                {
                    "email": "",
                    "type": "",
                    "primary": false,
                    "nest_uid": "1_1_1536657342_lyBhkbkDfGLp",
                    "checked": false
                }],
                "phones": [{
                    "phone": "",
                    "type": "",
                    "primary": false,
                    "nest_uid": "1_1_1536657342_CQPBBUBRZN",
                    "checked": false
                }],
                "nest_uid": "1_1_1536657342_fpTI2RF3XK",
                "checked": false
            }]
        }');
        
class Searcher {
    private $data;
    private $uid;
    private $result;

    public function __construct($data, $uid)
    {
        $this->data = $data;
        $this->uid = $uid;
    }

    private function search($data, $path)
    {
        foreach ($data as $k => $v) {
            if ($k === 'nest_uid' && $v === $this->uid) {
                $this->result[join('/', $path)] = $data;
            }
            if (is_array($v) || is_object($v)) {
                $subPath = $path;
                $subPath[] = $k;
                $this->search($v, $subPath);
            }
        }
    }

    public function getResult() {
        if($this->result === null) {
            $this->result = [];
            $this->search($this->data, []);
        }
        return $this->result;
    }
}

$searcher = new Searcher($innerdata, '1_1_1536657342_lyBhkbkLYT');
print_r($searcher->getResult());

Where is the comma of the line of first nest_uid