There doesn’t seem to be one well-known site dedicated exactly to “here’s the photo, here’s how it was edited” in the way you describe. A practical option is to post an example image in a photography community (with permission/right to share it) and ask how the look was achieved; often people can identify likely editing steps.

Also keep in mind that not every effect comes from Photoshop alone. Lighting, exposure, and other choices made when the photo was taken are often a major part of the final look.

For learning post-processing more broadly, books and training materials are a strong option. There are many resources covering general Photoshop editing as well as more specific topics like portrait retouching and HDR. Scott Kelby’s books and training materials are commonly recommended in this area.

So: no single definitive example-based site was identified, but community critique/forums plus good post-processing books are a solid way to learn.