Which position or body of the federal government would have the most power in determining whether a law is unconstitutional?

 The Supreme court          

Explanation:

According to the given question, The supreme court is one of the federal government position that have the most power to declare any type of unnecessary laws or the action as unconstitutional under the judicial reviewing process.

 In the article 3, the Constitution declare that supreme court give the responsibility for the purpose of overturn any type of law as unconstitutional in the united state in section 1.    

 Therefore, The supreme court is the correct answer.  

sumerians were responsible.

it's lower nubia : ) good luck