I'm assuming you mean from C++
Code:
CvPopupInfo kPopupInfo(BUTTONPOPUP_GOODY_HUT_REWARD, eGoody, iSpecialValue);
GC.GetEngineUserInterface()->AddPopup(kPopupInfo);
If you want a custom popup, you can use the BUTTONPOPUP_MODDER_x values and then write your own pop-up listener in Lua - take care if doing this as you must dismiss the popup correctly or you get the "bug" where popups randomly don't display