You'll need a list of logs to query. Chrome publishes their log list at: https://www.gstatic.com/ct/log_list/v3/log_list.json
My company offers a higher-level API for querying by domain name: https://sslmate.com/ct_search_api/
You can get the SHA256 fingerprint for your certificate by running
openssl x509 -in mycert.pem -sha256 -fingerprint -noout
openssl x509 -in mycert.pem -sha256 -fingerprint -noout | cut -d= -f2 | tr -d : | tr A-F a-f
If you need to do this against a web server and don't already have a copy of the certificate locally, something like
echo | openssl s_client -connect example.com:443 -servername example.com 2>/dev/null <&- | openssl x509 -sha256 -fingerprint -noout | cut -d= -f2 | tr -d : | tr A-F a-f
You'll need a list of logs to query. Chrome publishes their log list at: https://www.gstatic.com/ct/log_list/v3/log_list.json
My company offers a higher-level API for querying by domain name: https://sslmate.com/ct_search_api/