The groups are read from kleopatragroupsrc (located in the default location(s) for configuration files, e.g. next to kleopatrarc). The format is
[Group-<group id>] Name=<group name> Keys=<fingerprint>,<fingerprint>,...
where group id is a unique identifier for the group (can be identical to group name), group name is the (display) name of the group (which should also be unique for practical reasons), fingerprint is the fingerprint of a key in the group. Everything has to be UTF-8-encoded.