I've written a small python script that exports all groups and the related hosts within it (host, network, address range and security gateway objects) as a csv file. It also shows empty groups, that were possible forgotten about. The script works only for IPv4 objects!
# example csv header:
# groupname,groupuid,membername,membertype,memberip,membersubnetmask,memberuid
You can use the script and filter for the required group in the related group name column. The script usage is shown by specifying the -h parameter. Just make sure that you copy the whole folder within the zip as the subfolder "mgmt_api_lib" is also required (the script has only been tested with Python 2.7 - which is preinstalled within R80).