html page of my site

Please advise where to find html page of my site. I need to add a code of Google+. thanks

There is no html page.
Your site is dynamically generated from data in php files and database.
Template files can be found in /templates/TEMPLATENAME/

templates/gk_publisher /templatename, no exist, can you help more? Thanks

templates/gk_publisher
it is the folder where all theme files resists.

Where I can stick this?

Link your website
By adding a small line of code to http://zite7.com, you can have your Google+ page eligible to appear at the right of the Google search page when consultations on topics related and, thus, make your Google+ page easier to find. More information
Requests the webmaster of your website that you add the following line of code to the main page of your site:


<a href="https://plus.google.com/114678509679616797595" rel="publisher">Google+</a>

You could try /layouts/default.php but from your description I'm not shure where this code needs to be put and what should it do.

Where do I find the main index.php

I think You should check out file:
templates/gk_publisher/layouts/default.php
as index.php in main folder of template is used quite differently than on normal php sites.