Landry's owns the Golden Nugget. And almost all of the eateries in GN are Landry's restaurants....Chart House, Claim Jumper, the buffet.
If you look on the back of the gift card it tells you where you can spend it. You can use it on you hotel bill too.
I dont know if all the restaurants inside accept it...but I suspect (never tried) the ones that dont you could charge your bill to your room and pay with the gift card that way.