  We propose a new probe of cosmic relic neutrinos (C$\nu$B) using their
resonant scattering against cosmogenic neutrinos. Depending on the lightest
neutrino mass and the energy spectrum of the cosmogenic neutrino flux, a
Standard Model vector meson (such as a hadronic $\rho$) resonance can be
produced via $\nu\bar{\nu}$ annihilation. This leads to a distinct absorption
feature in the cosmogenic neutrino flux at an energy solely determined by the
meson mass and the neutrino mass, apart from redshift. By numerical
coincidence, the position of the $\rho$-resonance overlaps with the originally
predicted peak of the Greisen-Zatsepin-Kuzmin (GZK) neutrino flux, which offers
an enhanced absorption effect at higher redshifts. We show that this absorption
feature in the GZK neutrino flux may be observable in future radio-based
neutrino observatories, such as IceCube-Gen2 radio, provided there exists a
large overdensity in the C$\nu$B distribution. This therefore provides a new
probe of C$\nu$B clustering at large redshifts, complementary to the laboratory
probes (such as KATRIN) at zero redshift.
