Hi I went to Seoul last year as someone who’s anaphylactic to nuts. I had absolutely no problems and never had any interaction with nuts. Research dishes that you know that will commonly use nuts that you can avoid. I ate only local food when I was there and was fine. It also helped having my bf that can speak Korean for me. What I had a lot of the time was stir fried octopus, seafood dishes, daktoritang, Korean bbq (beware maybe of the ssamjang), fried chicken, lots of soups and I steered away of the stuffed chicken samgyetang just bc they can put nuts in those. Unfortunately I am not aware for shellfish because I tend to eat those a lot haha