What polyhedron has 3 vertecies?

Answer 1

None. The minimal vertex set from which you can construct a poly-n-chora is the n-simplex, or some deformation thereof, with n+1 vertices, as any n points fall in a single flat n-surface (that is unique unless the three points happen to also fall in the same n-1-surface).

Answer 2

A triangle is the only polyhedron that has exactly 3 vertices.