How do you define "praxeology"? My recollection from reading Human Action is it was only defined as "The study of human action."-- which could be scientific or might not be.

More specifically, as Mises conceives it, it is the study of the UNIVERSAL aspects of human action.

As used by the Austrian school, at least, it explicitly rejects empiricism, and uses deduction instead (from premises that are essentially taken for granted).

I will accept that.

But, I don't think it proves anything.

The scientific method is not an exclusive means to seek truth. Science has only one job-- to make testable predictions. It does not inform us about anything else.

You're essentially arguing "Falsus in uno, falsus in omnibus" because of an inherently illogical belief that only science can arrive at truth.

Rejecting empiricism means rejecting the very notion that one can make testable predictions, though. If that is rejected, what is the point of economics, even?

Austrian economics is essentially a deductive theology; the purpose is to work out the more detailed/complex implications of the basic axioms (both descriptive and, more importantly, prescriptive) that it assumes.