If you have not already look up some YouTube videos of people completing the challenges, this is not just to know how they are completed, but perhaps attention to timing that others used. I do actually remember one challenge that gave me a bit of trouble was I think gliding off Wayne Tower or something, it required a lot of tries. Or one that required shooting things in the Batmobile.
Have you completed all the other Riddler challenges in Arkham games? One comment I would make about the challenges in Arkham Knight is that it almost assumes you played all the other games, and challenges are often built off Origins, that are built off City, that are built off Asylum.
Some can be really tough, but they are not impossible, often I find that they require just changing your thought process for a bit. I assume you have already done some of the Batmobile death races, so you got past some of the most annoying ones.
_________________
Through dream I travel, at lantern's call
To consume the flames of a kingdom's fall