This is necro-ing an old question, but for people who see this question in the future:
Basic Global Position of Points:
"Global_position" is an object's position compared against root. The calculation for it is adding up positions so you know what a node's TOTAL position is when you ignore all the children-ing and parent-ing:
a.global_position = a.position + a.parent.position + a.parent.parent.position + ... + root.position
If you were to calculate the parent's global position it would also be:
a.parent.global_position = a.parent.position + a.parent.parent.position + ... + root.position
Using this, we can calculate any position by just adding the position with the global position of the parent! So:
a.global_position = a.position + a.parent.global_position
For this question, if we have a curve2D on a Path2D node, the points as global variables can be calculated as:
Path2D.curve.get_point_position(index) + Path2D.global_position
Yay!
Global Rotation:
The rotation quirk muddies this up a bit, since the curve points wouldn't rotate with the Path2D (probably. I haven't tested it). The probable solution would be to add the curve's position AFTER rotating it using Vector2.rotated:
Path2D.curve.get_point_position(index).rotated(deg2rad(Path2D.rotation_degrees)) + Path2D.global_position
For getting the entire curve, do a quick for loop over the curve and do this calculation on each one.
Happy coding!