Based on the information that a dog whistle has a high frequency, we can infer that:
It would have a high pitch.
High frequency corresponds to high pitch in sound perception. The other options regarding loudness, amplitude, and wavelength do not necessarily follow from the frequency alone. A dog whistle is designed to emit sounds that are inaudible to humans but can be heard by dogs, and it's the frequency (not amplitude or loudness) that determines the pitch.