The purpose of asking this question is that the interviewer wants to understand how you approach a given data problem and what is the though process you follow to ensure that you are organized. You can start answering this question by saying that you will start with finding the objective of the given problem and defining it so that there is solid direction on what need to be done. The next step would be to do data exploration and familiarise myself with the entire dataset which is very important when working with a new dataset.The next step would be to prepare the data for modelling which would including finding outliers, handling missing values and validating the data. Having validated the data, I will start data modelling untill I discover any meaningfuk insights. After this the final step would be to implement the model and track the output results.

This is the generic data analysis process that we have explained in this answer, however, the answer to your question might slightly change based on the kind of data problem and the tools available at hand.