ldns-keygen -a ED25519 example.com > zsk
ldns-keygen -a ED25519 -k example.com > ksk
...alternately, if you or your TLD prefer outdated key algorithms...
ldns-keygen -a RSASHA256 -b 1024 example.com > zsk
ldns-keygen -a RSASHA256 -b 2048 -k example.com > ksk