They are straight lines where two plane faces of the shape meet. The definition is sometimes extended to curved lines where curved (3d) faces meet such as at the base of a cone.
A Cube
A pentagonal pyramid has 10 edges.
The question is ambiguous. An octagon is a 2-dimensional shape with 8 edges and 8 vertices. Does a 3-D octagonal shape mean one with 8 edges or 8 faces or vertices, or faces which are 2d octagons?
There is no such 3-d shape if it also has flat faces.
A cube.
-12
The 3D shape formed by regular pentagons is a dodecahedron, which has 30 edges.
A sphere.
It is a cube or a cuboid
It is a cuboid
A cuboid, on its base, is a 3-d shape and four of its edges are vertical.
A triangular prism.A triangular prism.A triangular prism.A triangular prism.