what is the dimension of Black Hole? Black hole is the densest .... in universe. We know that dimension of universe is 4D . So, what is the dimensions of black hole? Is string theory explains what is it's dimension?
The singularity itself is, by definition, zero dimensional (well...you could argue one dimensional as it exists over time, but it has zero spacelike dimensions).

The event horizon is a two dimensional sphere, just like the surface of a beach ball - whether it can be said to have any thickness is unknown, there might be a thickness down at the Planck scale, but that's currently unknown.