I have Nginx on port 80 which handles abc.com, one.abc.com and two.abc.com.
For abc.com and one.abc.com, it redirects to Apache in port 8080.
For two.abc.com, it redirects to Apache in port 8081.

The task now is to upgrade to https.
Where to install the certificate - on nginx or on apache?
How does https calls hold good for the subdomains one.abc.comm and two.abc.com?

Sample nginx conf:
server {
listen 80;
servername abc.com, one.abc.com;
location / {
proxysetheader X-Real-IP $remoteaddr;
proxysetheader Host $httphost;
proxypass http://127.0.0.1:8080;
}
}

server {
    listen      80;
    server_name two.abc.com;
    location / {
        proxy_set_header   X-Real-IP $remote_addr;
        proxy_set_header   Host      $http_host;
        proxy_pass         http://127.0.0.1:8081;
    }
}

Thanks in advance.