State what Portia mean by "the will of a living daughter curbed by the will of a dead father" in The Merchant of Venice.

Shakespeare never met a pun he didn't like, and here Portia is punning on the two meanings of will: the word "will" both means desire and refers to a written document someone leaves after they die for the disposal of their money and goods.
In the first use of will, Portia refers to desire. She is saying her desire ("will") as a living daughter is curbed or thwarted by the legal document ("will") of her dead father.
Her father's will stipulates that Portia cannot marry whoever she pleases. She has to marry the man who correctly choses one of three caskets—one gold, one silver, and one lead—whether she likes it or not.
This is not the desire of Portia, who, like almost all young women, wishes to choose her husband on the basis of love and mutual compatibility, not a test devised by her dead father.