The question is not clear.
I assume that we are talking about the square faces on the surface of cube.
There are six square surfaces: On each surface there are two diagonals intersecting and they divide the square in to 4 equal triangles.
We can combine two adjacent triangles and we get 4 more triangles.
Each cube has (4+4) * 6 = 48 triangles.
Totally there are 48 * 4000 = 1,92,000 triangles.
I assume we are not to worry about the diagonals inside the cube - that can be between diametrically opposite corners on different surfaces. actually 4 diagonals can be drawn inside the cube meeting at the center of the cube. they also form 8 *2 =16 triangles (bigger than on the surfaces). If this number is included then we get 64,000 more triangles.