Calculating quantity containing the unit normal on the boundary with Discontinuous Galerkin

[dokken]

@Rania_Gian

stress = dot(grad(u), n) 
    #stress_project = project(stress, Vc) # this gives me error

This doesn’t make sense, as a standard projection is in L^2(\Omega), while the normal vector only lives on facets.
Also note that Vc should be discontinuous, as the gradient of a continuous space is discontinuous.

See for instance: Obtain velocity normal to boundary - #2 by dokken