fetch-ocsp-response is a Python script which performs OCSP query and get response. It uses openssl command under the hood. nghttpx uses it to enable OCSP stapling feature.
fetch-ocsp-response is a translation from original fetch-ocsp-response written in Perl and which has been developed as part of h2o project (https://github.com/h2o/h2o).
fetch-ocsp-response is usually installed under $(pkgdatadir), which is $(prefix)/share/nghttp2.