As an answer to my question to get licence information, servicedesk@geosn.sachsen.de (GeoSN) answered on Dec 3rd 2019
Sehr geehrter Herr Rouault,
selbstverständlich dürfen Sie alle unsere Daten nutzen.
Für die Nutzung der bereitgestellten Informationen des amtlichen
Vermessungswesens gelten die Bestimmungen der Datenlizenz Deutschland –
Namensnennung – Version 2.0 ([1]https://www.govdata.de/dl-de/by-2-0) unter
Angabe der Quelle (Namensnennung) „GeoSN“.
that is it is licensed under https://www.govdata.de/dl-de/by-2-0
"Data licence Germany – attribution – version 2.0" license listed by
https://opendefinition.org/licenses/ as a "Other conformant licenses", in the
same category as the license for the Canadian NTv2 grids we already have, and we must attribute it to the GeoSN source
The product NTv2_SN , to be downloaded at https://www.landesvermessung.sachsen.de/prod_fest_raum_fest/NTv2_SN_2014.zip (from http://www.landesvermessung.sachsen.de/download-5608.html?_cp=%7B%22accordion-content-4389%22%3A%7B%222%22%3Atrue%7D%2C%22previousOpen%22%3A%7B%22group%22%3A%22accordion-content-4389%22%2C%22idx%22%3A2%7D%7D ) , is the RD/83 -> ETRS89 transformation for East-Germany, and especially Saxony.
As an answer to my question to get licence information, servicedesk@geosn.sachsen.de (GeoSN) answered on Dec 3rd 2019
that is it is licensed under https://www.govdata.de/dl-de/by-2-0 "Data licence Germany – attribution – version 2.0" license listed by https://opendefinition.org/licenses/ as a "Other conformant licenses", in the same category as the license for the Canadian NTv2 grids we already have, and we must attribute it to the GeoSN source