If you want to read updates from your friend on Google+ with your RSS reader, here is how you can create the RSS feed in two easy steps.
1. Go to the friend’s profile on Google+. Find your friend’s numerical ID in the profile URL. It will look like this.
https://plus.google.com/106063395018684219722/posts
2. Paste this numerical ID at the end of this URL.
http://plus-one-feed-generator.appspot.com/106063395018684219722
That is all. Put this URL in your RSS reader and enjoy reading the feed.