"Где вилка?" if you mean "where is a fork?" instead "Вилка где?" if you mean "where is the fork?". The typical words order in Russian sentence is "from already known to unknown".
Former sentence "Где вилка" means that you search something, and, then, it is unspecufied fork.
Later sentence means that you are talking about already known fork, and then you ask about its position, and, not, for example, its temperature ("Вилка горячая?")