It looks like you were having the same problem I was having; finding a crystal clear explanation of how to enable SSI on NGINX. Crystal Clear entails not just which syntax to use, but the format, and exactly where to include it. I figured it out and it's not that difficult, but the lack of clear instructions on the internet was frustrating.
You'll need to open up the nginx.conf file and look for the section that is formatted as follows (I've included the 'ssi on' syntax as well):
location / {
root E:\website\FinalJRLWeb;
index index.html index.shtml;
ssi on;
}
It took me a bit to realize the location, but it's really as simple as adding the line 'ssi on' right underneath the specified index file names (and it should be able to really go anywhere you'd like, I don't imagine the order matters, just as long as it's within the two brackets {}).
After that, to verify that SSI is working on your NGINX server, add the following line anywhere in the 'body' tag of a blank html page
<!--#echo var="DATE_LOCAL" -->
and save it with the extension .shtml in your web server's root directory.
You should see the server's local date and time displayed upon visiting your page. I realize this is almost a year old, but after my frustration trying to find clear instructions, I wanted to do my best to try and provide clear instructions for anyone else that may need them. So hopefully this will help someone out!
Here's NGINX's documentation page on SSI (which honestly was not helping me as much as I would have liked, but it nonetheless is useful, and can only become more and more useful)
http://nginx.org/en/docs/http/ngx_http_ssi_module.html#ssi_last_modified