You are not actually doing anything. The GPU already culls any triangle that turns out to be outside the view frustum, faster than you could ever do it in a shader, right before the pixel shader stage. So you are effectively not doing any work. Frustum culling is done on the CPU side, not triangle by triangle obviously but either by big chunks of triangles (test the bounding box of those triangles, and if this bounding box is outside the frustum you don't even need to send all those triangles to the GPU via a draw call since they will end up off the screen), or via a quadtree/octree for maximum performance. The only point of frustum culling is to avoid sending the vertices to the GPU in the first place, along with doing useless vertex shader work for those vertices which won't end up being filled.

On topic however, you are trying to query the pipeline statistics of your GPU, which return information such as number of vertices sent to the GPU, number of vertices rasterized, number of pixels filled, etc... you should be able to find some code examples now that you know the keywords.