How to retrieve a list of entities without specifying rowKey from Azure Table Storage in the TableOperation?
Retrieve operation is for retrieving a single entity from Table Storage. This is why you will need to specify both PartitionKey and RowKey.
If you want to retrieve multiple entities (e.g. entities matching a particular PartitionKey value), the method you would want to call is CloudTable.ExecuteQuery and provide a query (e.g. PartitionKey eq 'your-partition-key-value') to that method.