The most question arise for every blogger who do not own a top level domain, do sitelinks get for sub domains. In that case yes, sitelinks get for sub domain but the blog should have unique content and must be useful for users.
Sitelinks are automatic and are generated basing on impressions and the page landing. To get sitelinks you need not work hard all you need to do is writing new content with related links, adding sub links under your post all helps to increase page visibility.
NOTE : The more the impressions you get the higher you get the sitelinks.
Here is the example of the blogspot.com site that got good sitelinks.