Something with an elastic waist :). I kid (somewhat). My experience has been that the attire at Chef Vola's runs the gamut from dressed to the nines to jeans. I usually go with dressy casual, but that's just me.
For pete's sake...it's in the basement of a house! Watch out for the pipes overhead and the walk through the prep area if you have to use the washroom. IMHO, this place is highly over rated and over priced.