What is the worldly punishment for a man who secluded himself with a woman (a widow) who is a stranger to him, in a car on a remote road, knowing that he is her cousin?

Being alone with a non-mahram woman is forbidden (haram). If no fornication occurs, then no prescribed punishment (hadd) is applicable. However, discretionary punishment (ta'zeer) may be imposed if the matter is brought before the ruler. Both the man and the woman must repent to Allah by abandoning the sin, regretting it, and resolving never to return to it. They should also conceal their sin. If they offer sincere repentance, they will not deserve punishment in the hereafter or in this world, because repentance erases what came before it.