The Report to track Sales Commissions is the Reports > Sales Commissions and Rebates Report.
In order to configure your products to track Sales Commissions, you will need to add custom attributes to your products (non-visible):
Sales Commission Gross Profit Percentage
Sales Commission Fixed Amount
Adding a Sales Commission Fixed Amount will assign that value as a Sales Commission for each order for that Sales Rep.
Sales Commission Gross Profit Percentage will add the specified value as a percentage of the SKU's price.
These fields can be updated in bulk via Import/Export.
Also note that this can be assigned on a product-by product basis, so not all products need to provide Sales Commission.