This example uses a basic cone. If it was created as a solid, and you try to node edit it, you will see that it cannot be selected.

Select the cone and open its Properties (see Object Properties). On the 3D page, select TC Surface.
Select the cone again, and click Explode (or select Format / Explode).
You can now node edit the cone nodes. ----Note: You also could have exploded the original solid object twice to obtain an exploded (node editable) surface.
Drag individual nodes to change the shape of the cone.

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