If you mean structural welding verification, then you need to evalute welding joints in NX postprocessing. Verification depends on the mesh used to model welding joint. You can use NX open to automize the welding verificaiton process in NX post.
NX Nastran is FEM solver used to solve stresses and displacement but welding verificaiton is usually done inside postprocesser based on IIW guids (for example).
If you mean Thermal verificaiton, NX Nastran can be used for welding thermal analysis, but you need to have a specific Heat Source for your welding process.