Topography in Revit can be tricky to manage for a number of reasons, but I would say the most limiting factor is that you can only input points (meaning, you cannot input contour lines or a mesh). If you do use a mesh or 3D lines to create a Topo, Revit simply takes the points from those elements and gives you no control in the generated mesh and contours.
This can be fairly frustrating, particularly if you are accustomed to Civil 3D, where you have control over these elements. Unfortunately, this is an issue that is hard-coded into Revit Topos, so until Autodesk decides to fix the Revit surface engine there isn’t much you can do (besides use other elements, which can be a partial solution).
Once the Topo is generated, you can extract the contour lines and underlying mesh elements by exporting a 3D view to dwg. And with Dynamo, you can extract all three Topo elements (points, contour lines, and mesh) entirely within Revit.
There are a few different nodes you can use to query Topo. The most obvious and easy to find are Topography.Mesh and Topography.Points. However, you can also use Element.Geometry to extract the contour lines as curves.
Since Revit contour lines are usually somewhat questionable, there might not be much use for isolating their curves, but you could quickly and easily create Model lines from contour lines.
But since Revit does not have polylines (like AutoCAD), all of the lines are created from individual segments.
The most useful of the three Topo elements are probably the points, which can be used to create geometry that “follows” grade, such as Hardscape/ Floors (see Make Hardscape Follow Topo).