How many edges and vertices does a rhombohedron have?

of vertices: 6 # of edges: 5

There are several kinds of 'isohedrons', http://mathworld.wolfram.com/Isohedron.html However if you meant 'icosahedron' then it has 30 edges and 12 vertices.

The number of edges and vertices ina polyhedron will depend on the polyhedron one selects either to study, build or etc...

One edge (boundary) and no vertices.

A cylinder has 0 vertices. If an edge is defined by the meeting of two faces then there are two edges but if an edge is defined by the meeting of two PLANE faces then there are 0 edges.