What is the ruling on someone who comes late to the mosque and finds a funeral prayer; should he pray the Dhuhr that he missed, or should he pray the funeral prayer first?

Consider if the remaining time is sufficient for both the Dhuhr prayer and the funeral prayer. If so, perform the funeral prayer first, then Dhuhr. If there is only enough time to perform Dhuhr, then one must pray Dhuhr, even if it means missing the funeral prayer.