To use any Watson service inside Node-RED you will need to instantiate an instance of the service from Bluemix. The services can then either be bound or unbound to your Node-RED application. If they are bound then when you add the service node to your flow you will not see options to enter credentials as they are obtained by Node-RED from Bluemix.

When you add a node for a service that you have not bound into your application then you will be prompted to provide service credentials.

You obtain these service credentials from Bluemix. Select the unbound service in your Bluemix dashboard

to see the service credentials