Most Asus MoBos, at least ones I have used label the pin headers. If ya can't find your specific model, you can also try looking for something close as vendors try and minimize parts inventories and will use the same pin arrangement on mutiple models.
I looked at the P755D for example
Page 2-39 shows a picture of the thing an it shows the two pins for the reset to be the two furthest to the right in the bottom row (in bold text)
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Going from left to right, bottom row, on this mobo they are:
Pins 1 & 2 = HD LED
Pins 3 - 5 = nuthin
pins 6 & 7 = power switch
Pin 8 = nuthin
Pins 9 & 10 = reset switch