Within a Custom Report, you can both breakdown and filter your data by SKU.

To add SKU as a breakdown within your Custom Report, select "Breakdowns" and search "SKU". This will automatically break down your data by SKU in the leftmost column of your table.

To filter your data by a certain SKU within your Custom Report, select "Filters" and "Add filter". From there, search "SKU" and select. You can filter by a certain SKU by clicking on the filter and adjusting the dropdown to "is" instead of "contains", and checking the SKU you need.