I'm fairly sure we know the functions of at least most of the proteins in the human body, or in any body.
I'd have to partially, at least, disagree. We likely know one or two sort of obvious functions for a large number of proteins in our bodies, but that is liable to be only a tiny fraction of all the various things some of them do. And I would be surprised if we have any more than a description like "olfactory receptor" for the majority of the 25,000(??) proteins our bodies make.
We're quite a ways from Frankenstein.