What are the evaluation metrics for evaluating testing data

I am doing a project using T5 Transformer. I have read documentations related to T5 Transformer model. The aim of the project is to generate Job Description based on Job_Role and Skills. My concern here is which metric can I use for evaluating predictions.

While training data I am using loss metrics but for predictions I am not sure which metric can I use.

Any resources or read material is appreciated. Thankyou.