On the 21st they were trying to get some momentum back and did some protesting on the Champs Elysées, but really, I wouldn't be worried about much impact at all, if any. As the previous commenter said, it's on Saturdays, so that already limits impact.
If you're very concerned, you could try checking this website as well (Google Translate if you need it in English). When you click on the manifestation you want more info about, you can see what they know if anything yet, including meeting place, time, and potential metro stops impacted. For the 28th, for example, they don't have any info yet about location.
But generally, just don't worry. You've always got a good chance at seeing SOME kind of demonstration somewhere in Paris, but that's just kind of normal and not a big deal. I remember the first time I ever went to Paris thinking I was so lucky to get to see some kind of protest, not realizing just how common that is!