I want to know how much profit I made from a single customer
That is a difficult thing to determine, often impossible. You would have to allocate all your expenses proportionally among all your customers according to some scheme. I suspect you really want to know something much more specific and limited. Please describe exactly what you are trying to determine. Also describe the type of business you are conducting.
I think you may want to explore the “Divisions” feature.
Setting divisions as a project you can see the profitability.
You could in theory get the average profit of each item and multiply that by the corresponding items sold to a customer.
That would only give a gross profit figure, not net profit.
The gross profit can be easily calculated through a custom report.