Search Console, formerly Google’s Webmaster Tools (WMT), gives you a simple way of checking what kind of queries your site is showing up in the organic listings for, but the most useful thing is probably the indexing status updates and any crawling issues encountered by Google bot.
This guide also tells you how to upload your subdomain’s sitemap onto Search Console.
- Sitemap naming and location
There is no need to name the sitemaps differently, as they are located on separate subdomains (if you instead had a directory structure, you would need to name the sitemaps differently). Also, it is recommended that the sitemaps reside on the subdomain root and NOT within any kind of directory, as all URLs within the sitemap must be on the same host.
E.g http://dogs.seokitty.net/folder/sitemap.xml would not be able to include any URLs on the dogs.seokitty.net subdomain which do not use the /folder/ path. So don’t chuck it in there.
Sitemap declaration in robots.txt
(each subdomain requires its own robots.txt)
The robots.txt file for each subdomain requires the sitemap specification, added as a line in the robots.txt. The full location needs to be added, using the following syntax:
So you might have a robots.txt for your subdomain that looks like this:
- Creation of subdomain Searh Console properties
Each subdomain requires its own Search Console property in order to ping Google with the new sitemaps. In the Search Console homepage, click the ‘Add a Property’ button on the top right.
Input the full subdomain URL with its protocol, and you will be asked to verify ownership of the subdomain.
This can be done by using a sign in to the domain name provider, or can be confirmed by linking to a Google Analytics property of the same subdomain. On the whole, confirming it through the DNP is usually the easier way of going about this. Aside from these, the above methods require uploading a verification file onto the server or the editing of onpage HTML.
All your subdomains will need their own seperate verification.
- Notify Google of sitemap location
Once the sitemaps are on each subdomain, they can be declared to Google within the Search Console. Within the ‘crawl’ tab, click ‘Sitemaps’. This will be empty.
Click the red ‘Add a sitemap’ button on the top right and type ‘sitemap.xml’ into the popup box, then click submit.
If successful, ‘item submitted’ will appear on a yellow banner above the viewer.
Google may not crawl the sitemap instantly – it can take anything from an hour to a day for the sitemap to be crawled.
- Indexing checks
Once a sitemap is uploaded to each of the subdomain Search Console properties, the status of indexing can be checked within the ‘Google index’ tab, on ‘index status’.
If you’ve just created your subdomain, this will increase and level out following its publication - but it’s worth keeping an eye on any considerable drops or sudden increases.
The crawl errors tab also requires monitoring following the subdomain publication. This is found within ‘crawl’ and then ‘crawl errors’.
Here will be listed any server errors, soft 404s, denied URLs or 404 errors. These may require manual checking after you’ve set up your new site.
That’s it! :3
 Source: http://www.sitemaps.org/faq.html