Your question is Investigate Model Overfitting. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
You've trained a model that looks very strong on the training set, but the team is worried it may not generalize well to new data. You want to verify whether the model is learning real signal or memorizing patterns from the training sample.
How would you investigate whether a model is overfitting?