ElliotDX made a mod that unhides the hidden skills. It was a nice mod, but it's not been updated since before Late Night came out, so I made my own.
This mod will unhide all the hidden skills. This means you will see a progress bar over your sim's head like when they are gaining any other skill. They also will show up in you sim's skill journal. They don't have a real icon, but rather just a fading dot and when you check them in the skill journal, they will be labeled as "Hidden _____ Skill." You also won't receive a award certificate for mastering these skills.
Read more and download at Mod The Sims
