A very interesting question that I also have pondered before. In the first episodes it is mentioned that she needs to mask the human scent as Vulcans find it revolting.
Ergo she does not smell "human"
I would think that human scent is a combination of all our secretions however miniscule they are up to the famous old people smell.
So the question arises. What is the Vulcan urinary tract like? How do they sweat if at all, saliva - tons of it? Vaginal secretions? Tears? Earwax?
How much of all this is documented in trek lore?
But now that I have ruined our image of T'Pol and reduced her to a bunch of glands on two lovely feet I want to finish with this.
In my dreams there is a sweet flowery scent that fills my entire universe as she gets closer and whispers " I find you agreeable Surak"