To send data to other IoT platforms, which node I should use?
HTTP response, HTTP response,WebSocket out Or MQTT out
It depends what protocol the iot platform supports.
What iot platform are you using?
MQTT would be a strong candidate. Also http (REST api) is available
It also depends on what architecture you have in mind; everything is local on the same local network or should connection be made via internet?
According to their docs, Thinger supports a number of different protocols. So you could use either the MQTT Out node to publish messages to their broker, or the HTTP Request node to send the data via HTTP.