how can i implement ReportState and ChangeState in smart home skill.

Hello. To take a step back, StateReport events and ChangeReport events are two separate but related types of responses you can send. Let's begin then by defining each.

StateReport Event

When you open the Alexa app, go to the "Devices" tab and tap on a specific device, Amazon will send you a ReportState directive every three seconds. You respond to each ReportState directive synchronously by returning a StateReport event.
https://developer.amazon.com/en-US/docs/alexa/smarthome/state-reporting-for-a-smart-home-skill.html#report-state-when-alexa-requests-it

If you do not respond to a ReportState directive with a StateReport event, then you will see the "Device is Unresponsive" message in the Alexa app.

ChangeReport Event

For ChangeReport events, you're not responding to a request sent by Amazon. Instead, you're proactively reporting a change in a device's state to Amazon as a result of some interaction which occurred outside of the Alexa app. These ChangeReport events are sent by making an API call to the Alexa Event Gateway.
https://developer.amazon.com/en-US/docs/alexa/smarthome/send-events-to-the-alexa-event-gateway.html

For example, if I physically turn off a switch, I might want to send a ChangeReport event to the Alexa Event Gateway so that Alexa is aware of the device's change in state. Implementing this change reporting will also allow you to create routines in the Alexa app based upon these changes in state.

As a note, ChangeReport events are optional and can only be sent for device interfaces where "proactivelyReported" was declared as true in the Discover.Response JSON.

Python - Responding With StateReport

Now, to your question of how to create JSON responses using Python. A JSON object is basically just a set of key-value pairs. Within Python, you would create a similar object by making a dictionary.

Because Python dictionaries and JSON aren't 100% the same, you'll want to use the Python "json" module to convert your dictionary to JSON before returning it.

More information on the Python JSON encoder and decoder can be found here:
https://docs.python.org/3/library/json.html

Code Snippet

Here's a sample from my own code used which is used to build a StateReport response to a ReportState directive for a lock device.

import json

...

def build_LockStateReport(correlationToken, BearerToken):
    LockStateReport = {
        "context": {
            "properties": [
                {
                    "namespace": "Alexa.LockController",
                    "name": "lockState",
                    "value": "LOCKED",
                    "timeOfSample": get_utc_timestamp(),
                    "uncertaintyInMilliseconds": 0
                }
            ]
        },
        "event": {
            "header": {
                "messageId": get_uuid(),
                "correlationToken": correlationToken,
                "namespace": "Alexa",
                "name": "StateReport",
                "payloadVersion": "3"
            },
            "endpoint": {
                "scope": {
                    "type": "BearerToken",
                    "token": BearerToken
                },
                "endpointId": "lock-appliance-001",
                "cookie": {}
            },
            "payload": {}
        }
    }
    print("StateReport Response: ", json.dumps(LockStateReport))
    return json.loads(json.dumps(LockStateReport))

Python - Sending A ChangeReport

As with your response to a StateReport, you'll want to convert the Python dictionary that you define to JSON before returning it.

However, since this is a proactive report, you're not synchronously responding to an event sent to your Skill's Lambda function. You therefore must make an API call in your Python code.

The module I like to use for this purpose is "requests". You can learn more about "requests" in the following documentation:
https://docs.python-requests.org/en/master/

The specific headers and body Alexa will expect for a ChangeReport is defined here:
https://developer.amazon.com/en-US/docs/alexa/smarthome/send-events-to-the-alexa-event-gateway.html#message-contents

https://developer.amazon.com/en-US/docs/alexa/smarthome/state-reporting-for-a-smart-home-skill.html#changereport-event

Code Snippet

Similarly, here's a code snipped that I was able to use to proactively report to the Alexa Event Gateway that my "lock-appliance-01" device changed its "lockState" to "UNLOCKED" as a result of a physical interaction:

import requests
import json

url = "https://api.amazonalexa.com/v3/events"

payload = json.dumps({
  "event": {
    "header": {
      "namespace": "Alexa",
      "name": "ChangeReport",
      "messageId": get_uuid(),
      "payloadVersion": "3"
    },
    "endpoint": {
      "scope": {
        "type": "BearerToken",
        "token": "Atza|token-redacted"
      },
      "endpointId": "lock-appliance-001"
    },
    "payload": {
      "change": {
        "cause": {
          "type": "PHYSICAL_INTERACTION"
        },
        "properties": [
          {
            "namespace": "Alexa.LockController",
            "name": "lockState",
            "value": "UNLOCKED",
            "timeOfSample": get_utc_timestamp(),
            "uncertaintyInMilliseconds": 1000
          }
        ]
      }
    }
  },
  "context": {}
})
headers = {
  'Content-Type': 'application/json',
  'Authorization': 'Bearer Atza|token-redacted',
  'Host': 'api.amazonalexa.com'
}

response = requests.request("POST", url, headers=headers, data=payload)

print("Status Code:" + str(response.status_code))
print("Response:" + response.text)

I realize this is a long response but, it's a big question and I hope this information helps get you started!