i have successfully configured the city based sub domains, but issue was that
when i type city.domain.com its working fine, and also when i click cities in footer then also working great,
but when searched from search bar, the it was not redirecting to city.domain.com  how it make work?

its possible?

if its possible how to rectify this?

@Ghany
Is there any pattern or function specific for city-based engine?

yeah
http://prntscr.com/gg7m4o

you know very well then me.

@Ghany
That is just setting.

URLs for items in autocomplete are generated in file:
oc-content/themes/veronika/contact.php

line:
$prepare[$i]['item_url'] = osc_item_url_ns($prepare[$i]['pk_i_id']);

As you can see it's osclass core function. You may need to add some parameters here, not sure. What is sample URL for any listing that leads to subdomain?