I think it will be "잘 모르겠습니다(jal mo-reu-get-seum-ni-da.)" meaning "I am not sure of it." or "I have no idea." \^o^/

I think you mean this phrase: "잘 먹겠습니다" [jal meok ge sseum ni da], which means something like "Enjoy your meal", but literally translated it means "I will eat well". You can learn more about it here: http://www.talktomeinkorean.com/lessons/l1l12/ Good luck ^_^