If an employee has a court-issued restraining order against an individual, that person cannot contact her or come within a specified distance in person. This includes contact with the employee at work as well as at home and in public. Therefore, an employee may inform you that she has had a restraining order issued to someone and that person knows where she works.
The employee is not required to tell you why the order has been issued, so do not ask. She may choose to volunteer the information, which is fine. Ideally, she will give you the name and a description of the person and a copy of the restraining order to help in your efforts to keep the person away from the workplace. If the company has a switchboard operator or receptionist, ask the employee for permission to advise these workers as well since they may be the ones to have initial contact with callers and visitors seeking out the employee. If the employee shared information about why the restraining order was issued, you may not forward this information to anyone else on staff.