In u.trust LAN Crypt, encryption keys are linked to a group, but you can link them to any group you like later on. In this step you should choose a group to which all the imported keys will be saved.
The “Special Groups Root Node” is the root group of u.trust LAN Crypt. At your discretion, create a “SGN-Import” group in the u.trust LAN Crypt administration and choose that group as target.
It makes sense to use the comment field of the key to document which keys were imported, regardless of which group they will be in.