i.e., the points within green region.
Is such data included in the .obj file?
If yes, how can I read such data from the .obj file?
If no, is there any other way to obtain the points’ position within the green region?
You have the NavMesh, so you technically already have all of the points within it, because you have the 3D geometry, so you could test within the exported/found mesh.
That said, you might want to try the UNavigationSystem class. In here there are numerous methods to project a point onto the NavMesh, or return a random point within the bounds.
However, any method providing all the points would not likely be of value, because FVector is made up of floats, so you would have a huge array of values that would be valid, with only tiny changes in their value.