BAPI is just a function module, there is no such thing as some kind of specific "BAPI knowledge". But clueless employers love to put it in the job descriptions. BADI implementation is not a rocket science either.
But I would be rather suspicious of someone who worked with ABAP for 2 years and have not learned anything about BAPI or BADI. This might indicate that either the candidate has no curiosity / desire to learn or they are not able to learn on their own, without someone motivating them or explaining. These are not very desirable qualities for a developer IMHO.