Where do witnesses sign?
Will makers should sign their will at the end of it, after the final clause. 
The witnesses then sign their name below the will maker’s after having watched the will maker (testator) make their signature or acknowledgement first. All three should use the same pen. An example of a typical layout is shown opposite. The witnesses should write their full name, occupation and contact details.
As said above the signatures of the willmaker and witnesses should be on the last page of the will. It is prudent that the signatures are not the only thing on the page if at all possible.
There is no particular legal requirement for where witnesses must sign.
Should signatures be made at the bottom of each page?
While technically not a requirement that the bottom of each page of the will is signed, to do so is a safeguard against page substitutions. The usual signing procedure is followed. First the will-maker signs their name in the presence of both witnesses. Then using the same pen, each witness signs their name, everyone being present together throughout.