Can a person go to the graveyard of the prophets & sufi saints and pray for them and ask to fulfill our wishes?

We can’t mixed Prophets with other Sufi Saints. Allah has given this authority to Prophets to fulfill our wishes even if they are not alive in this world. As our deeds are being present to them so they can listen our wishes too. But as fa as a Sufi Saint is concerned, one can pray for them and even one can visit to their grave and recite the Holy Quran for them if he was really a true devotee of Allah and not the one whom people have raised without any reason then yes he can ask his wishes from Allah with their Wasila (source) too.