[BorisJe]

<pre id="out"></pre>
<script>
    				let obj =
    				{
    				"$id": "1", "id": 34, "dateTimeAdd": "2021-12-11T16:45:12.0015098", "cash": 70, "listCoinsChanges":
    						{
    						"$id": "2", "$values":[
    										{
    										"$id": "3", "id": 52, "cost": 10.00, "quantity": 2, "order":
    												{
    												"$ref": "1"
    												}
    										}
    								]
    						}
    						, "productId": 9, "product": null
    				} ;
                   let arr = obj.listCoinsChanges.$values;
                   out.append(JSON.stringify(arr, "", 1));
                   out.append(`\n cost : ${arr[0].cost}`);
                   out.append(`\n quantity : ${arr[0].quantity}`);
    </script>

Спасибо но в listCoinsChanges может быть больше 1 элемента от 1 до 10-15