I do not know how to answer your specific question. I will share this long post on setting up SSL for DSS.
In that post, I think I understand that there are two files used to configure DSS nginx and localhost Nginx. The one is controlled in /etc/nginx/nginx.conf and the /etc/nginx directory. The are other files in the DSS_DATA directory that have an impact on this. To get SSL to work I had to tell the DSS Nginx server to only talk to the host wide Nginx reverse proxy server.
I also found this page of SOME additional help. https://doc.dataiku.com/dss/latest/installation/custom_install.html
That said you may need some support from the support team on these issues. I know that I did.
There are my $0.02. Hope this is a little bit of help.