Catalyzes the hydrolysis of queuosine 5'-phosphate, releasing the nucleobase queuine (q). Is required for salvage of queuine from exogenous queuosine (Q) that is imported and then converted to queuosine 5'-phosphate intracellularly. In vitro, can also catalyze the release of the q base directly from Q as substrate; however, it was shown that Q is not the biologically relevant substrate. Shows a very low activity on queuosine 3',5'-diphosphate, and cannot release q from queuosine 3'-phosphate and from the 5'-nucleotides AMP, UMP, CMP or GMP, indicating specificity for the queuine base (PubMed:36610787). Can complement the yeast mutant SPAC589.05c, restoring Q incorporation into tRNA (PubMed:24911101). {ECO:0000269|PubMed:24911101, ECO:0000269|PubMed:36610787}. This is the function of QNG1 (Q-nucleotide N-glycosylase 1, ENSG00000165118).