How many inches above a window should the curtain rod be mounted?

Basically goes by what you prefer. Everyone is different

The style now is what ever you want. Tape a pc. of string over your window to see where you want it. Good luck.

https://www.realsimple.com/home-organizing/decorating/curtains-window-treatments

It is popular to hang as close to the ceiling as possible.....

have curtains touch floor!! This would be used in a living room... bedroom...... etc..... maybe not for kitchen!!

Height of your curtain rods depends on several factors. #1) How long it is your curtain. #2) Is the window in direct view of the sun or is it on the shaded side of your home? Windows that face the sun might require that you install the curtain rod 6" above the top of the window or even as close as possible to the ceiling. It depends on the amountof light you want to enter the room. Is it a bedroom or a living room? Will a guest ever be sleeping in that room? Be sure to buy room darkening curtains and not just sheers.