How do I add an action to watson conversation response?

You can use context variables or action variables for that.
How to use context variables? Add in your Advance response the “context” and the values, check my example.

I’ve used the conversation simple for that.

In your Watson Developer Cloud – IBM Bluemix – Watson Conversation, add in the Advanced response this JSON example, Assuming it is in this conversation node that your application will do something:

{
  "context": {
    "verified": true;
  },
  "output": {
    "text": {
      "values": [
        "Please wait and I'll verified your request."
      ],
      "selection_policy": "sequential"
    }
  }
}

Example (app.js):

function updateMessage(input, data, req, res) {
  if (data.context.verified === true){
    searchRequest(data, req, res);
    } else if (data.output && data.output.text) {
    return res.json(data);
    }
    return data;
}

You can use the data for sending something within conversation flow.

function searchRequest(data, req, res){
    // something to do and return value
    var sendRequest = "Thanks for wait, the request is" + valueRequest;
    data.output.text[0] = sendRequest;
    return data;
}

EDIT:

You can add one JSON object like “action”, and your code will recognize this variable, with the same example that @Mikko said. And you can check this with:

data.output.action === 'close'

• See more about Context variables.
• See more about Building a dialog.