Basics. Knowledge of tools and their use. They usually ask you to demonstrate your proficiency with an instrument or tool. ( I did an interview and the guy gave me a Vernier Caliper and wanted a demonstration).
It's *good* to have qualifications if you want to do an apprenticeship - particularly good passes in maths and English.
If you lack qualifications you may have to get good enough scores on literacy and numeracy tests in order to be considered and/or you might have to do additional English and maths study during your apprenticeship.