Answer: vertical line at 0.
Explanation:
In a closed economy, investments from other countries do not come in and the country does not invest in other countries. This means that capital is neither flowing in nor out.
Net capita outflow is the difference between capital flowing in and capital that is flowing out. If there is no capital flowing in nor out then net capital outflow will be 0. On the graph described, net capital outflow will therefore be zero for all real interest rates which will create a vertical line at 0.