How can we access device data sent to Watson Iot platform from any device. We want to access the data via Web/Window Application and show it on our page.
I'm not sure I completely understand your question, but it sounds like you want to view the event data from a device and display it in your web application.
An application can connect to the Watson IoT Platform and subscribe for events from a device in the same org. Refer to the documentation for developing applications for the Watson IoT Platform.
Subscribing to device events
An application can subscribe to events from one or more devices, for example:
Subscribe to topic iot-2/type/device_type/id/device_id/evt/event_id/fmt/format_string
Note: To subscribe to more than one type of event or to events from more than a single device, use the MQTT "any" wildcard character (+) for any of the following components:
device_type
device_id
event_id
format_string