How many edges are in a prism?

There are 9 edges in a (triangular) prism.

Other prisms have different number of edges.
It depends upon the cross-sectional shape of the prism.

If n is the number of sides to the cross-sectional shape of the prism, the number of edges is 3n.

A triangular prism has 3x3 = 9 edges

A rectangular prism (cuboid) has 3 x 4 = 12 edges

etc