Oh, Gosh, I could write you a book on that.
Short answer: all over. According to the courts, the Necessary and Proper Clause justifies laws against bribing or killing federal agents or officials. The Tax Clause justifies criminal penalties for tax evasion. The power to establish the Post Office justifies laws against committing fraud by use of the mails. The 13th Amendment justifies laws against human trafficking. The Commerce Clause justifies the law against interstate shipment of obscene movies. And so on.
Where do they get the EPA from, or any of the “czars” and federal jurisdiction for any of those things? The executive branch is supposed to enforce the laws established by Congress. But if Congress has no authority to tell a farmer he has to pay fines for his cows farting, then how can the EPA have that authority? How can the feds say that if I’m going to have a doctor see me in my own hometown I have to first sign a statement saying that the clinic has permission to tell the feds anything they want to know about what they learned about my body? How can the feds record every phone call I make?
See, none of that seems to be an enumerated power. So where do they get all this from?