Is ablution required for a visitor to graves? And what is the supplication for the deceased in the graveyard?

Ablution is not obligatory for someone visiting graves because visiting graves is not among the matters that require purification. As for supplicating for the deceased, it is narrated from the Prophet, peace and blessings be upon him, that he said: "Peace be upon you, O inhabitants of these abodes, from among the believers and Muslims. And verily, God willing, we shall join you. We ask God for well-being for us and for you," and his saying: "Peace be upon you, O dwellers of the graves. May God forgive us and you. You are our predecessors, and we are following in your footsteps." If one visits a specific grave, he should greet its occupant just as he would greet the living, placing the grave between himself and the Qiblah. If he then supplicates for him and seeks forgiveness for him, there is no harm in that.