すみません、このお弁当に卵は入っていますか？ — Excuse me, does this bento box contain egg? (Convenience · Store, Formal — to staff, JLPT N4)

Gesture & etiquette

Point to the specific item on the shelf and then point to your mouth or make a 'questioning' face.

Be aware that even if an item doesn't list a specific allergen, cross-contamination is possible. Always double-check if your allergy is severe.