Here’s a guide on adding OCSP to your Plesk 11.5.30 or Plesk 12.0.18 Panel.
Firstly you need to create a file containing both your intermediate and CA certificate, lets call it domainCA.pem.
create the folder…

# mkdir /etc/ssl/ocsp/

and upload domainCA.pem to it.

Now create a file called ocsp.inc in

# nano /etc/sw-cp-server/conf.d/ocsp.inc

and add the following nginx directives to it…

ssl_stapling on;
ssl_stapling_verify on;
ssl_trusted_certificate /etc/ssl/ocsp/domainCA.pem;
resolver 8.8.4.4 8.8.8.8 valid=300s;
resolver_timeout 10s;

Next you need to add an include statement for ocsp.inc in the plesk.conf file…

# nano /etc/sw-cp-server/conf.d/plesk.conf

Like so…

include conf.d/*ocsp.inc;

With the other include directives.

And restart the Plesk server with

# service sw-cp-server restart

You now have OCSP on your Plesk Panel.

You can also add these directives on a per domain basis in the Plesk Panel under

Plesk -> Domains -> yourdomain.tld -> Apache & Nginx Settings -> Additional nginx directives