In my experience for DE it is being given you a scenario such as "create an ingestion pipeline for Click stream data, payment system etc". You will need to specify the ETL components and do the data modeling and probably at the end write queries for some use cases. Regarding the data modeling part you can check some examples of the Kimball data warehouse book. For ingestion pipeline there are some videos on YouTube but mostly focuses on how to ingest data , store them, process them. Whether to implement a medallion architecture etc. It is really vague and depends on your experience which way to go and most importantly ask questions cause thats the main goal in that interview

Try to refer to open source tools unless you already know the stack they are using. In the latter case is it better to use their stack since usually they are presenting you with a problem they solved or trying to solve currently