Man pages matching name gnutls_global_set_log_level in section 3:

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