In the GPU tab on the task manager, click on the label for one of your graphs (Copy, Video Encode, Video Decode, etc) and switch it to show CUDA. I found that my CUDA utilization was consistently between 100% and ~70% when rendering, which makes sense if Arnold is just using CUDA (speculation on my part), and means my card (1080 ti) was just about maxed out. With my CUDA cores at 100%, Windows was still reporting the overall GPU at like 3%, so it seems like Windows just doesn't approximate utilization in the way we'd like it to for Arnold.
Since you have a 2070, it may be using Tensor cores alongside/instead of CUDA, so you may have the option to show Tensor cores in task manager? I can't speak for that, but dig around.
The Windows Task Manager isn't reliable for Arnold GPU, use another tool, like GPU-Z to monitor the GPU usage
Which DCC/plugin are you using? There's instructions for maya and c4d here:
https://docs.arnoldrenderer.com/display/A5AILIC/Check+the+Arnold+Log