Potential ADA accommodations abound, but a few declared 'unreasonable'
There's no exhaustive list of potentially reasonable accommodations for employees with disabilities. Whether an accommodation is reasonable will depend on the unique circumstances of each instance, including the individual's limitations and essential job functions. Some accommodations, however, have been declared "unreasonable."
3 unreasonable accommodations
It isn't reasonable to eliminate job's essential functions. An essential function is a "fundamental duty of the position." It's a central component of the job in question. When determining whether a function is essential, courts will typically consider (1) the identification of particular duties or functions in job descriptions or advertisements, (2) the amount of time spent performing the function, and (3) the number of employees available to perform it, among other factors.
Under the Americans with Disabilities Act (ADA), the purpose of an accommodation is to enable an employee to continue performing the essential job functions. Thus, the Equal Employment Opportunity Commission (EEOC) has long advised an employer "does not have to eliminate an essential function, i.e., a fundamental duty of the position" as an accommodation. You can typically reject any request to do so on the grounds it isn't reasonable for ADA purposes.
It isn't reasonable to place employee in position for which he isn't qualified. Transferring an employee to a different position may constitute a reasonable accommodation. But he must be qualified for the position, i.e., have the education, experience, and/or skills necessary to perform the new role.