How to get GVL comments via API from data Layer

https://127.0.0.1:8443/automation/api/v2/nodes/plc/app/Application/sym/GVL_Test/bTest

This is like you have seen only getting the data.

The comment is part of the metadata. So you have to read them:

https://127.0.0.1:8443/automation/api/v2/nodes/plc/app/Application/sym/GVL_Test/bTest?type=metadata

The answer will be in my case:

{
  "type": "object",
  "value": {
    "nodeClass": "Variable",
    "operations": {
      "read": true,
      "write": true,
      "create": false,
      "delete": false,
      "browse": true
    },
    "description": "This is a test boolean",
    "descriptionUrl": "",
    "displayName": "",
    "displayFormat": "Auto",
    "unit": "",
    "references": []
  }
}

For more information about using the REST API see "Using REST API of ctrlX CORE".