What is the standard height for a vertical grab bar next to a toilet?

usually it will be placed according to request because many elderly or handicapped have different situations.

the grab bar can be placed horizontally, diagonally, or vertically-- and the height can start from about 28 inches off the floor or higher for taller persons.

ADA Horz bars are 34 to 36" to the centerline of the bar. If you are mounting in an ADA location you have to get it right. The commode and bars have to go where they have to go. Do your research.