Grill bratwurst, covered, over medium heat, turning frequently, until meat is no longer pink, 15 – 20 minutes.
Grill onion, covered, until lightly browned, 3 – 4 minutes on each side.
Cut bratwurst into 2-inch pieces.
In a stockpot, combine water, beer and seafood seasoning; add corn, potatoes, lemon, bratwurst and onion; bring to a boil.
Reduce heat; simmer, uncovered, until potatoes are tender, 15 – 20 minutes.
Stir in cod; cook until fish flakes easily with a fork, 4 – 6 minutes; drain and transfer to a large serving platter.
Sprinkle with pepper.
