Check if a vector3 is on a gridgraph

Beginner Questions
#1

Hi,

is it possible to have a Vector3 (e.g. via Random.insideUnitSphere) and check whether that point is on a gridpgraph or not? I see graph.PointOnNavmesh exists, but that seems to only work for Navmeshes.

#2

AstarPath.active.GetNearest(pos).node.Walkable