There is no hard fast rule. There are general guidelines. In the end it's where YOU like them, where they can be reached easily and where several will look balanced on the cabintry throughout the room.

I suggest you get some art putty and see where you are happy with them both to reach them and looking at a distance with several in place.

Thank You Lucidos for your suggestions.

My Kitchen ceiling is 13 feet high and I am doing double top cabinets with flat wood as first row and glass cabinets on top.
Since these glass doors are above the 37-1/2" top wood cabinets I am worried how the placement of pull with effect the look....and I am skeptical if I go with 3" or 3-1/2" from the bottom edge of the door for placing the pulls vertically...
Any suggestions is appreciated.....

Some options I'm throwing at you:

No pulls and have the doors touch open. On my double stacked cabinets I have no pulls on the upper cabinets there is a magnetic push catch when I touch the door it opens. The look is less fussy and makes the mullion cabinets appear contiguous.

You can also opt to put a pull as opposed to a handle....

Buy a Cabinet Hardware Template, one for doors and one for drawers. Some even come with a drill bit. This is essential when drilling. If you can't use the art putty as suggested above, make a paper cutout of the hardware and experiment with various placements. The best distance is what pleases you the most.

Thank You so much lucidos and catlady999 for your thoughtful suggestions... I finally picked a pull and a knob combinations.... I am installing knobs on the top glass cabinets which are very small 14"wx11"h .. and pulls on other taller cabinets.. glass and wood... lower side... as shown by lucidos pic above....
Once everything is done, I will post the pictures...thanks again..