You have to use json.loads not json.dumps.

Try this:

import json

event = {
   "Records":[
      {
         "messageId":"916f5e95-b2f6-4148-9c62-2ac8e764f06c",
         "receiptHandle":"AQEBmLuoGWtLtFFgvyCFdSPMJh2HKgHOIPWNUq22EOwCzGT8iILZm97CE6j4J6oR71ZpDr3sgxQcJyVZ+dmmvGl+fFftT9GCJqZYrjMGsR2Q6WsMd8ciI8bTtDXyvsk8ektd7UGfh4gxIZoFp7WUKVRcMEeBkubKd8T4/Io81D0l/AK7MxcEfCj40vWEsex1kkGmMRlBtdSeGyy7fJgUq5CFAYWciiWtbSit8S0Y38xZPmsIFhoxP0egQRoJcW4aUgMi469Gj5+khizetybtgC8vux5NCg/IejxcCueXkQ7LKVF8kfRdqRSUYB6DsOrGgfmZpK4wpXIarByNz0R2p7J88meYpj2IVULv/emXsSYaKG4rXnpbH4J9ijbLWckYLAd7wPDzCYri1ZSTgAz0kchsEw==",
         "body":"{\n\"name\": \"aniket\",\n\"tag\": \"hello\"\n}",
         "attributes":{
            "ApproximateReceiveCount":"1",
            "SentTimestamp":"1602046897707",
            "SenderId":"AIDAR3BXDV4FCWXL56NUU",
            "ApproximateFirstReceiveTimestamp":"1602046897712"
         },
         "messageAttributes":{

         },
         "md5OfBody":"98da683a47692b39c1d43bd4fa21ed89",
         "eventSource":"aws:sqs",
         "eventSourceARN":"arn:aws:sqs:ap-south-1:126817120010:documentation",
         "awsRegion":"ap-south-1"
      }
   ]
}

parsed = json.loads(event['Records'][0]['body'])
print(json.dumps(parsed, indent=4, sort_keys=True))

Output:

{
    "name": "aniket",
    "tag": "hello"
}

In your lambda function you should return a response object with a JSON object in the response body.

# Lambda Function
def get_json(event, context):
    """Retrieve JSON from server."""
    # Business Logic Goes Here.
    response = {
        "statusCode": 200,
        "headers": {},
        "body": json.dumps({
            "message": "This is the message in a JSON object."
        })
    }
    return response

Try

import json

def lambda_handler(event, context):
    body = json.loads(event['body'])
    return {
        'statusCode': 200,
        'body': json.dumps(body['data'])
    }

I'm not sure if this is what you want, but you can just do 'body': json_data. I tested this now in my λ function:

Lambda function

import json

def lambda_handler(event, context):

    json_data = [{"Dp_Record_Id": 2, 
                  "DP_TYPE": "NSDL",
                  "DP_ID": "40877589", 
                  "CLIENT_ID": "1232", 
                  "Default_flag": "Y"}]

    return {'statusCode': 200,
            'headers': {
            "Access-Control-Allow-Origin": "*",
            "Access-Control-Allow-Methods": 'GET, POST, PUT, DELETE, OPTIONS'
            },
            'body': json_data
        }    

Result

Response:
{
  "statusCode": 200,
  "headers": {
    "Access-Control-Allow-Origin": "*",
    "Access-Control-Allow-Methods": "GET, POST, PUT, DELETE, OPTIONS"
  },
  "body": [
    {
      "Dp_Record_Id": 2,
      "DP_TYPE": "NSDL",
      "DP_ID": "40877589",
      "CLIENT_ID": "1232",
      "Default_flag": "Y"
    }
  ]
}

So there are 3 problems:

Problem 1: In your example event, ['Records'][0]['Sns']['Message'] is a str in JSON format. That means that you need to parse to a dict like this:

 message = event['Records'][0]['Sns']['Message']
 message = json.loads(message)

Problem 2: message['Trigger']['Dimensions'] is a list but you are trying to access it like if it were a dict. So you only need to change your code to:

message = message['Trigger']['Dimensions'][0]['name']

Problem 3: Message is a str that means that you need to verify that is a plain str or json str (otherwise you are going to have problems with multiple structures and types). For that your code could look like:

 message = event['Records'][0]['Sns']['Message']
    if isinstance(message, str):
        try:
            message = json.loads(message)
        except Exception as e:
            print(e) # Or do nothing, this is just to log the error
    elif isinstance(message, list):
        message = message[0]
    # Maybe evaluate bool, tuple, etc other types

    print('RESPONSE', message['Trigger']['Dimensions'][0]['name'] if isinstance(message, dict) else message)

However I would also recommend to make it more extensible iterating the elements that you know are list. And for safety reasons (trying to avoid null pointer exceptions), use the get() function with a default value. http://www.tutorialspoint.com/python/dictionary_get.htm . Try maybe to create a function to parse structures and make it reusable.

Good luck!

When you invoke the lambda locally or through the Lambda console, you are invoking that lambda directly and so your lambda receives exactly what you're sending.

When you invoke it through API Gateway, API Gateway creates the event object for you based on your HTTP request. It adds the HTTP headers, path, query strings, payload, etc.

Here's a summary of what you're getting as an event from an API Gateway invocation:

{
    "resource": "Resource path",
    "path": "Path parameter",
    "httpMethod": "Incoming request's method name"
    "headers": {Incoming request headers}
    "queryStringParameters": {query string parameters }
    "pathParameters":  {path parameters}
    "stageVariables": {Applicable stage variables}
    "requestContext": {Request context, including authorizer-returned key-value pairs}
    "body": "A JSON string of the request payload."
    "isBase64Encoded": "A boolean flag to indicate if the applicable request payload is Base64-encode"
}

Reference: http://docs.aws.amazon.com/apigateway/latest/developerguide/api-gateway-set-up-simple-proxy.html#api-gateway-simple-proxy-for-lambda-input-format

As you can see, the body will be sent to you as a string which you can parse using json.loads().