Man pages matching name curlopt_ssh_knownhosts in section 3:

CURLOPT_SSH_KNOWNHOSTS.3.en	debian 10 / libcurl4-doc
CURLOPT_SSH_KNOWNHOSTS.3.en	debian 11 / libcurl4-doc
CURLOPT_SSH_KNOWNHOSTS.3.en	debian 12 / libcurl4-doc