The origin and nature of cosmic rays at very high energy (UHECRs) is a long-standing puzzle that is still not completely resolved after a century of theoretical and experimental efforts. Neutrinos can travel untouched from their source, thus indicating their locations. Neutrinos of cosmic origin are expected to be produced via the decay of charged pions and kaons, generated in hadronic interactions of cosmic rays with gas or radiation in their acceleration sites or during their propagation.