Mentees' technical backgrounds can vary quite a bit, depending on whether they're recent graduates, or experienced software engineers looking for a career change.
However, there are a few baseline skills that you should expect any mentee to have (with rare exceptions): they should be comfortable with Python, as well as basic data manipulation and model building libraries like Pandas and scikit-learn.
Exceptions could be made if, for example, you have a candidate who is very experienced in R, or one who is targeting certain kinds of data analytics positions that aren't as Python-heavy. But in general, we strongly recommend not taking on a mentee whose core coding skills aren't solid.