What punishment did portia impose shylock?

None. She was not the judge (although she is called a "judge" by the Duke, who is the real judge) and did not have the power to sentence Shylock. She did, however, advise the court that in her view Shylock fell under a statute which imposed a sentence of death or such lesser sentence as the court might see fit on an "alien" who made an attempt on the life of a citizen of Venice.