getbakedpoints () is an array of positions. To count them use the property of arrays: size. I leave you a small example that duplicates a mesh and puts it in each point of the array, that is, the baked points of the curve. If you reduce the bake interval in the path properties you can see how the points increase.
extends Spatial
var points
func _ready():
points=$Path.curve.get_baked_points()
print(points.size())
for i in points:
var a =$MeshInstance.duplicate()
add_child(a)
a.translation = i