I work part-time at a nursing home. After knee surgery, I have a dr note to return to work for 3 hours a day but the nursing home has refused to put

You probably do not have a legal right to force your employer to put you back on the schedule with reduced hours.  While your knee surgery may well mean you qualify for protection from discrimination as a person with a disability (the law also prohibits discrimination against you based on your employer's perception that you are disabled, or because you have a medical history of disability), you may not be able to perform the "essential functions" of  your job, which includes working a full shift.  Many employers provide "transitional work" for persons who are unable to resume their full duties for a short period of time, but your employer may not.  In addition, while an employer might be required to accommodate your condition, it may be unreasonable to require the employer to allow you to work a reduced schedule for a variety of reasons.