First adjust the diopter to your eyes, This is the sliding mechanism above/behind the rubber eye-piece!
Lens must be on the camera of course, I take that for granted. When you press the release-button halfway down you can even adjust the diopter so you can see the numbers displayed more or less sharp!
First it looks black at the bottom but as soon as you press the release-button halfway down, an AF-lens will then focus and you right away see the results i.e. data as shown here:
Exposure value in viewfinder - PentaxForums.com
After a while the bottom becomes black again.
But once I had a heavy used K10SD here were this part in the view-finder which shows you the data (can anybody let me know the name of this in English please)
somehow got unglued, one could see that it got lose and some numbers were very difficult to decipher.
I don't know where one would have access to this part to fix it.
Anyway, if you don't see any data at all or very dim, something is wrong because it is clear enough that one can read the data very well!