Man pages matching name gnutls_certificate_get_peers_subkey_id in section 3:

gnutls_certificate_get_peers_subkey_id.3.en	debian 10 / gnutls-doc
gnutls_certificate_get_peers_subkey_id.3.en	debian 11 / gnutls-doc
gnutls_certificate_get_peers_subkey_id.3.en	debian 12 / gnutls-doc