So the flat, planar sketch which defines the limits of the pad, not the upper/lower bounds of the adjacent topo. You’ll want to pull the associated topography element instead, as that contains two meshes which are a bit easier to work with than the entire site. From there you can get the geometry, convert to a polysurface, and use topology to pull the edges which only have one adjacent face. The result:
This will contain two resulting loop sets: One for the building pad’s sketch lines, and one for the topography’s walls. For completely cut pads or completely filled pads these produce two loops, which can be grouped and filtered by height. For pads which are retaining on both sides things get messy as the curve loops overlap. You can simply filter out edges with the most common Z heights at both ends to remove the ‘pad edge’ from the set. This should get you one curve loop for the lines where the building meets the land, from which you can pull whatever points you’d desire.