Is there any airport for domestic flights in Panama?

Absolutely.  From Panama City there is the Albrook Airport (Marcos Gelabert Airport), located in the Albrook Area.

There are some other airports in other provinces like Contadora Island, Isla San Jose  (both in the Pearl Islands), Bocas del Toro, Changuinola, David, Colon, La Palma/Sambu/El Real/Yaviza/Jaque (in the Darien province), Chitre, Santiago, Pinas Bay, Achutupu/Aligandi/Povenir/Playon Chico/Ustupu (San Blas Archipelago).