An employer may not ask whether a prospective employee has a disability that may affect his ability to perform a job.  An employer certainly can determine the qualifications necessary to successfully perform a job, but cannot ask directly about the existence of a disability.

In the event the prospective employee indicates that he has a disability that may require an accommodation, however, things change slightly.  At that point, an employer may ask what types of accommodations would allow the prospective employee to perform the functions of the job.