@jack3661mao, you need to internalize your data before uploading the GH file, otherwise the geometry won’t be available for other people!
That said, you can usually get the normal vector at a curve parameter by calculating the cross product between the tangent vector at the parameter and for instance the world z-axis.
If a given Brep edge is the folding edge, then (for tol to t-tol) get the tangents at t - tol, t + tol (tol: a user defined value, maybe the doc tol maybe not) and their CrossProduct.