I understand now that:

In French there is no “like” as in English. Something doesn’t smell like chocolate, it just “smells chocolate”.

So, you would say: Ça sent le chocolat

But how would you say "Who smells chocolate?" 

Qui sent le chocolat ?

Whereas Qu'est-ce qui sent le chocolat is the longer way of saying "What smells like chocolate" 

Is this correct?

Or would you have to say something like: qui peut sentir le chocolat ?