The measurement of the complex impedance response and accompanied power absorption <$E P( omega )> in the radiofrequency and microwave ranges represents a most popular experimental method to investigate pinning mechanisms and the vortex dynamics in type-II superconductors. In the theory, the pinning potential (PP) well for a vortex must be a priori specified in order to subsequently analyze the measured data. We have theoretically solved the inverse problem at T = 0 K and exemplify how the coordinate dependence of a PP can be determined from a set of experimental curves <$EP( omega | j sub 0>) measured at subcritical dc currents <$E0~<<~j sub 0 ~<<~j sub c> under a small microwave excitation <$Ej sub 1 ~<< <<~j sub c> with frequency <$Eomega>. We furthermore elucidate how and why the depinning frequency <$Eomega sub p>, which separates the non-dissipative (quasi-adiabatic) and the dissipative (high-frequency) regimes of small vortex oscillations in the PP, is reduced with the increase of <$Ej sub 0>. The results can be directly applied to a wide range of conventional superconductors with a PP subjected to superimposed dc and small microwave ac currents at <$ET~<< <<~T sub c>.