A qualified individual with a disability is a person who has the skills and education to perform the essential functions of a job with or without reasonable accommodations as long as the reasonable accommodations do not present an undue hardship to the employer. 42 U.S.C. § 12111(8)
"Reasonable accommodation" and "undue hardship" are two key terms in the ADA. Employers should know when to ask if a reasonable accommodation is needed. After explaining the hiring process, an employer may ask all the applicants if they will need a reasonable accommodation to assist them in completing the application process.
During the hiring process and before a job offer is extended, an employer should not ask an applicant if a reasonable accommodation is needed to perform essential job functions unless the employer knows that the applicant has a disability. An employer may know about a disability because it's obvious or the applicant may have voluntarily disclosed the information.
When an applicant is hired, the employer may ask if a reasonable accommodation is needed to perform the job but all new employees in the same job category must be asked this question.