Hi! despite that's my hometown I don't have many recomendations for you (I have emigrated over 7 years ago and many things have changed). Anyway I have 2 places that definitely you should visit
FIrst is a really good restaurant with traditional polish food - Swojski smak
Second is an enchanging cafe where definitely you should try Tiger tea and their amazing warm apple pie served with ice cream - Szarlotka. The place is called Pi kawa
Then I have heard of one place where they serve pierogi (they serve those in many restaurants but this one is dedicated to pierogi). I havent tried it out myself but if you'd like to try here is the address:
Oh, and this is not food related but it's a place worth visiting even if you are not keen on museums ;
)Amber museum http://www.mhmg.gda.pl/international/...
Hope you'll find those links helpful
Have a great time in Gdansk :)