scale and zero point are the quantization parameters for the layer. They are used to quantize the weight from fp32 to int8 domain.
re-quantization scale is defined based on input, weight and output scale. It is defined as
requant_scale =  input_scale_fp32 * weight_scale_fp32 / output_scale_fp32
The conversion from accumulated int32 values to fp32 happens in the quantization backends, either FBGEMM or QNNPACK and the requantization scale can be found there.
cc @dskhudia