Ahmed.T

I have also heard of some guys stacking two knock sensors on top of each other with a long bolt/stud through both.  I have never tested it personally but assuming you have nice flat parallel coupling surfaces on top and bottom I would expect it to work ok.

Hello Ahmed
Above the headers seems no good place to me, because there's a good chance that temperatures wil get to high, and wiring or knock sensor itself is gonna melt, imho.
My experience is, that the best placement of the sensor is on the intake side, as close as possible to the center of the block.