dV is a measure of how much your spacecraft can accelerate. In an environment with nothing but your spaceship, you might be able to accelerate to 2,000 m/s before running out of fuel. So your ship's dV is 2,000 m/s. You could do something similar by editing a craft into orbit and doing a maneuver node with more dV requirement than your ship, then measuring how much dV is left in the maneuver node after you run out of fuel.