I can display a 3D surface with z-axis {z,-100, 15000}: Plot3D[n2U[v, n], {v, -100.0, 20.0}, {n, 0.0, 1.0}].
I can plot a 3D line: ListLinePlot3D[mydata] which has z-axis {z, -100, 12000}. The line happens to lie on the 3D surface but that is not relevant to the question:
How can I display the 3D surface and the 3D line in the same 3D cartesian coordinate system?

Plot3Dand theListLinePlot3D? – bmf Jan 09 '23 at 05:12Show[Plot3D[x+y,{x,-1,1},{y,-1,1},PlotStyle-> Green], Graphics3D[{Red,Line[{{-1,-1,-2},{1,1,2}}]}]]Adjust that as needed. – Bill Jan 09 '23 at 07:31