Description of problem: dnf repoquery doesn't have --groupmember as repoquery of yum .
I create a pull-request that implements requested option (https://github.com/rpm-software-management/dnf/pull/848).
libdnf-0.9.3-1.fc26 dnf-plugins-core-2.1.3-1.fc26 dnf-2.6.2-1.fc26 has been submitted as an update to Fedora 26. https://bodhi.fedoraproject.org/updates/FEDORA-2017-6f4c06b2d7
dnf-2.6.2-1.fc26, dnf-plugins-core-2.1.3-1.fc26, libdnf-0.9.3-1.fc26 has been pushed to the Fedora 26 testing repository. If problems still persist, please make note of it in this bug report. See https://fedoraproject.org/wiki/QA:Updates_Testing for instructions on how to install test updates. You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2017-6f4c06b2d7
dnf-2.6.2-1.fc26, dnf-plugins-core-2.1.3-1.fc26, libdnf-0.9.3-1.fc26 has been pushed to the Fedora 26 stable repository. If problems still persist, please make note of it in this bug report.