code: def get_service_account_email(self, project=None):
          
          if project is None:
              project = self.project
          path = "/projects/%s/serviceAccount" % (project,)
          api_response = self._connection.api_request(method="GET", path=path)
          return api_response["email"]
docs: Get the email address of the project's BigQuery service account
  
          Note:
              This is the service account that BigQuery uses to manage tables
              encrypted by a key in KMS.
  
          Args:
              project (str, optional):
                  Project ID to use for retreiving service account email.
                  Defaults to the client's project.
  
          Returns:
              str: service account email address
  
          Example:
  
              >>> from google.cloud import bigquery
              >>> client = bigquery.Client()
              >>> client.get_service_account_email()
              my_service_account@my-project.iam.gserviceaccount.com