In the reduce stage of a MR script, how do I get the value (which is summarized) of, for example, of field 1 and field 2 in the following object that I get in the reduce stage to process?

{
  "recordType": null,
  "id": "1",
  "values": {
    "GROUP(field1)": {
      "value": "123",
      "text": "Test123"
    },
    "SUM(field2)": "43.00"
  }
}

try

object.values["SUM(field2)"]

Yes, just did, that does the trick, I was getting confused. Thanks!

I'd recommend a different label that doesn't include special characters

By special characters you mean the ( ), right?

Yea, I'd try to give that entire

SUM(field2)

a friendlier/meaningful name, same with

GROUP(xxx)