What son did Bathsheba bear David after their first child died?

Answer: Solomon

After the child died, David comforted Bathsheba; she gave birth to a son, and they named him Solomon.

“Then David comforted his wife Bathsheba, and he went to her and lay with her. So she gave birth to a son, and they named him Solomon. Now the LORD loved the child”— 2 Samuel 12:24 (BSB)