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To generate ksqlprocessinglog and forward the error message to a Kafka topic, follow these steps:

1. Set up a Kafka cluster and install the Confluent Platform.

2. Launch the KSQL server and create a Kafka topic for storing the error messages.

3. Use the CREATE STREAM statement to define a KSQL stream based on the data source, and specify the schema for the stream.

4. Use the SELECT statement to perform a query on the stream, and include the LOGGING clause to generate ksqlprocessinglog.

5. Use the EMIT CHANGES clause to forward the error messages to the Kafka topic.

For example:

CREATE STREAM orders (order_id INT, product_name VARCHAR, amount INT)
  WITH (KAFKA_TOPIC='orders_topic', VALUE_FORMAT='JSON');

SELECT *
  FROM orders
  WHERE amount < 0
  LOGGING 'error_log'
  EMIT CHANGES;

In this example, we create a stream called "orders" based on a Kafka topic called "orderstopic". We define the schema for the stream as having three fields: orderid, productname, and amount. Then, we perform a query on the stream to select all orders where the amount is less than zero. We include the LOGGING clause with the identifier "errorlog" to generate ksqlprocessinglog. Finally, we use the EMIT CHANGES clause to forward any error messages to a Kafka topic called "error_log".