If you are request productSku, you should be pairing it with itemRevenue. This effectively gives you the revenue brought in by a specific product.
If you want transactions and transactionRevenue, you can pair them with transactionId.
If you're trying to figure out how many transactions a specific product was in, you'd have to break down productSku by transactionId and do a unique count of transactionId at the productSku level (which isn't an available metric).