I’m not sure that I understand your question; is it the exact form of the vowel mark in the name of God that concerns you?
If so, see pp. 21 and 27 of arabdoc.pdf for getting the “dagger alif” in
arabtex. I don’t know whether you can get it in
arabtex without using the ASCII input notation.
arabxetex, you can get it, at least in some readily available fonts, by typing the unicode character
FDF2 directly, as ClintEastwood suggested: see the second line of my example. You can also get it by letting a well designed font handle the ligature, as in the third line of the example below. The first line, from your example, seems to break the font’s automatic recognition of the ligature by explicit input of the shadda.
% must be compiled with xelatex
There are many more details about this particular ligature in section 3.3.1 of the documentation for
arabxetex, including comments about the behavior of various fonts.