I just did a quick Google and found this list of hidden traits for you.
I am not sure how you could see if your sim has any without Nraas MC but perhaps someone else can help you there.
Only MasterController (together with its MC Cheats module) can reveal or change hidden traits. They are on the Sim >Advanced >Traits menu along with regular traits, except they get an "H" designation for being Hidden. It's the same with hidden skills and there are tons of those.
Comments
I am not sure how you could see if your sim has any without Nraas MC but perhaps someone else can help you there.
Zumi and the Winchester Brothers
The Watcher's Caretaker - A Limited ISBI
NRaas has moved!
Our new site is at http://nraas.net
Free Toddler and Kids Items | 100% FREE store items| Missing Store Stencils