Job Interview Questions That You Can and Can't Ask Under the ADA
The U.S. Equal Employment Opportunity Commission (EEOC) is the federal agency that enforces the ADA.

According to the EEOC, you should never ask the following questions in a job interview:

Have you ever had or been treated for any of the following conditions or diseases? (Followed by a checklist of various diseases or conditions.)
List any conditions or diseases for which you have been treated in the past three years.
Have you ever been hospitalized? If so, for what condition?
Have you ever been treated by a psychologist or psychiatrist? If so, for what?
Have you ever been treated for any mental condition?
Do you suffer from any health-related condition that might prevent you from performing this job?
Have you had any major illnesses in the past five years?
How many days were you absent from work because of illness last year? (You may, however, tell the applicant what your attendance requirements are and then ask the applicant if she will be able to meet those requirements.)
Do you have any physical defects that preclude you from doing certain types of things?
Do you have any disabilities or impairments that might affect your ability to do the job?
Are you taking any prescribed drugs?
Have you ever been treated for drug addiction or alcoholism?
Have you ever filed a worker's compensation claim?

According to the EEOC, you may ask the following questions in a job interview:

Can you perform all of the job functions?
How would you perform the job functions? (If you want to ask any applicant this question, you should ask all applicants this question.)
Can you meet my attendance requirements?
What are your professional certifications and licenses?
Do you currently use illegal drugs?