How to associate onnx with pytorch code

I tried to port a pytorch trained model to a RockChip 3566 using rknn toolkit.
I am able to torch.onnx._export my pytorch model to model.onnx successfully.
When building the model.rknn for RK3566 inference using the rknn toolkit from model.onnx, I encounter an error:

Fatal: Meet unsupported operator: Sqrt(name=“Sqrt_941”).

I am curious where this “sqrt” operator came from in my original pytorch code/model. I did a “grep -r sqrt *.py” in my development folders and cannot find any sqrt function in my code. Is there a way/tool can help me to associate this “Sqrt_941” in model.onnx to my original pytorch code? and how?

Thanks a lot for your help.