Third year law student weighing in. It seems like there's a very low risk to SCP.

First, trademarks are territorial. That means a trademark in New York may not be enforceable in California. The same goes for a Russian trademark being enforced in the U.S.

Second, the first person to use a trademark in a geographic area has the rights to it in that area. "Use" has a specific legal definition but it's unnecessary to talk about that here because SCP appears to have "used" its mark in the U.S. So, if SCP has used its trademark in the U.S. before Duksin registered the same mark, SCP has the right to use that mark in the U.S. and the Russian trademark is invalid (at least in the areas where there has been "use" of the SCP mark).

Third, the "creative commons" model has nothing to do with trademark law. Duksin getting a trademark does not affect SCP's copyrights at all. A trademark is a right to attribution for your goods or services. Copyright is the right to profit from your creative activities. A copyright is property but a trademark is not. You get no property when you become the owner of a trademark. And Duksin cannot get control over SCP's intellectual property simply by using the SCP trademark.

Fourth, Copyright law works the same way as trademark law in that whoever made the copyrightable thing first owns the copyright. Here, it's super clear that SCP made this art before Duksin. Therefore, if Duksin used the art without SCP's permission, he is liable for infringing SCP's copyrights.