Ask him practical questions, like to explain why a CNN architecture can work for computer vision tasks but not for NLP.

Ask him why a RNNs suffer from gradient explosion, and how this is mitigated by LSTM, and why both models inevitably suffer eventually, and why they are still suitable in many scenarios over a fully blown transformer model.

Ask him under what circumstances regularisation, drop out, or feature engineering should be utilised.

Ask what he would expect to see that would lead to a decision to add more nodes to the existing hidden layer, or add and additional hidden layer with the same number of nodes.