Hello @yogendrasgautam - Thank you for posting your query. Dashboard doesn’t contain any information about the columns or calculated columns. You need to run the describe_analysis_definition / describe_dataset API Calls in order to get those details. You can programmatically run these methods and save the json output. Hope this helps!
https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/quicksight/client/describe_analysis_definition.html
https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/quicksight/client/describe_data_set.html