First of all, please use titles for your questions that already tell readers what your question is about. "How to implement spherical gravity" would have been a better title. Also, the tag "help" doesn't really help others understand which category your question falls into.
Next, your question does not show that you have tried at least one or two approaches on your own. Most forums don't work in the way that users cry for help and just get their work done for them.
Lastly, be as precise as possible when describing your plan. I still don't get what you want to do. Is it supposed to be a simulation where the car follows a pre-defined track? Then you might want to take a look at Godot Docs under Your first game, where a Path2D node is used to spawn enemies. Maybe using a similar technique you can have your car follow that track.
Or is the car user-controlled and of the sphere only part is ever shown so that your project rather resembles a racing game? Then you might get some ideas from following people like HeartBeast on YouTube, who, among other things, discuss such aspects of Godot.