Setup
There are 3 ways to configure COGS in Klar (Shopify, Sheet, Average Value), see this article on the setup and how they are defined & calculated.
Analysis
To see what the COGS for a specific product / SKU in Klar are, do the following:
Go to the "Revenue & Profit" Flex Table to the Profitability tab
Set the first dimension to "Product SKU"
Set the metric display to "Per Item"
Now you can compare the COGS values for each SKU with the values entered in Shopify / the sheet.