The only skl to step conversion that is perhaps doable, is export of skeleton data from Autodesk Maya files (.skl) to STEP format, probably in effort to export the geometry or similar data. Everything points Maya being the only software that can be used for this, so if you for some reason struggle with this export, or need something specific, it might be best to reach out to the Maya online community or Autodesk support.
Updated: October 26, 2023