yup bro
why second only site is ranking and how to improve
I think you are a funny character. Yes, all the content is the same. Sure the themes are different, but why would you expect a domain to rank for the search term of a different domain without some convoluted interlinking activity or some way of helping G see they are related?
It seems you expect that simply because they are hosted on the same IP, and have the same content that somehow G should think 1.domain.com is naturally related to domain.com as a search query, but this conclusion would be very illogically drawn in this situation. The fact of the matter is that your domains have no direct relationship to each other besides the content, and the primary domain is NEVER mentioned anywhere on the sub-domain, so why do you think G hasn't put it together?
Anyway my new friend ... when G puts it together ... none of your content is going to be ranked for any queries at all, so good luck with this activity. You can't post the exact same content like this on multiple domains and expect to have good outcomes unless your traffic source is not organically generated by search results. I can definitely see uses for this kind of thing, but it does seem your approach is likely to end badly based on my own past experiences. Nonetheless ... we all have to run our own tests.
Good luck!
P.S. If this is really how you want to do this, you could use SNAP Social Networks Auto Poster to use the feed of the primary domain as the content generator for the sub-domain. Then by configuring SNAP to actually use the correct source information as the author - it will link back every post to the original post on the primary domain. However, as I suggested above, I believe this will have bad outcomes regardless of how you utilize this "duplicate content" across multiple domains particularly those hosted on one primary IP address.
