To assess a candidate's practical knowledge of machine learning, consider including a coding or machine learning project in the interview process. Provide them with a real-world problem and ask them to develop a machine-learning model. Evaluate their approach to data analysis, feature engineering, model selection, and evaluation metrics.
Additionally, consider discussing their experience with specific machine learning algorithms, their understanding of data preprocessing techniques, and their ability to handle common challenges in model development. Their ability to communicate their thought process and explain complex concepts will give you valuable insights into their practical knowledge.