Training of waitstaff on food allergens is essential, but the entire establishment should maintain an allergen-free kitchen and incorporate a company-wide food safety culture.
Understanding and implementing food allergen labeling is essential and following an in-house plant allergen control plan will help to mitigate cross-contamination.
Unlike foodborne infections that strike without warning, folks who have food allergies (or food intolerance) generally know of them and avoid the offending ingredients.