There isn't really an SE site for challenging a theory, per se. If you want to publish some content stating counterarguments to evolution, SE isn't a good place to do that.
The point of SE's Q&A format is that people ask questions that other people might later also have, and people leave answers that will help other people in the future. Unlike most forums, it's not a quick "I ask a question and get an answer, and we all forget about it" - we want to build a permanent repository of information for the internet forever (or however long, anyway).
Thus, if there is a legitimate question, you might be able to find a site. Just "challenging evolution" doesn't really fit into a question so I can't think of any site right now that this would belong to.
Note that you can actually post a fact - when you are asking a question, you have the option to answer it yourself and post both at the same time. In fact, this perfectly demonstrates how SE differs - on a normal forum site, why would you answer yourself? If you already know the answer, why would you ask? But on SE, if you have an answer to a problem you think others might have, that isn't already asked, you are more than welcome to ask that question yourself and provide your answer such that people in the future who come across it can be helped too.
Do keep in mind that you must respect the site's scope, on-topic definition, and question/answer quality control. I would recommend checking a site's tour and help center before you post there, if you find a site that would be suitable.
Anyway, if you format this into a proper question (and/or answer), it may be easier to identify an appropriate target site to post that, but from this information alone, it doesn't seem within the scope of SE as a whole.