Deuces, bienvenidos to the Forums! You've posed an interesting question, and the manual doesn't provide a direct answer, that's for sure.
I'm not sure about the answer, either, but here's what I'm able to figure out from the information that is provided:
Assuming you shoot at the K10D's maximum resolution of 3872X2592 pixels, you get 10,036,224 pixels in your image file.
The 2.5" LCD can display 210,000 pixels. If you divide, 10,036,224÷210,000=477.92, or about 478 pixels in the file map to one pixel on the LCD display. However, the display is set at default to give a 1.2 times magnification (roughly 398 file pixels per display pixel). The default can be increased up to 20 times magnification (roughly 24 file pixels per display pixel).
Now, when I am in playback with a default magnification of 1.2, and am clicking the rear e-dial through its range, I count 17 steps of increasing magnification. The steps are clearly not doubling the display magnification with each click, and I don't know/can't calculate the step increase without some fancy measuring on the screen. (I sure didn't try it, as I don't want to start a career as a nefarious measurebator! The math above is dangerously close enough!
) At maximum, it doesn't look like I'm particularly close to 1:1.
I tried increasing the menu setting (in the Custom menu) for initial magnification to the maximum of 16 times, just to see what would happen. On playback, I just got fewer clicks on the rear e-dial to reach maximum magnification; two clicks (16X and 20X) was it!
So, if I'm understanding things right, the most you can get out of the K10D's LCD display is about a 24:1 ratio between max resolution file pixels and display pixels. For 1:1 pixel peeping, get thee to a computer!