In the federal court system, which court would have original jurisdiction concerning the violation of a federal law?

The Supreme court.

Explanation:

The Apex court in the country, that is the Supreme Court of the United States is the only court saddled with the responsibility of having original jurisdiction concerning the violation of a federal law.

The part at which the constitution gave the Supreme Court original jurisdiction concerning the violation of a federal law can be found in Article III, Section 2 in the Judiciary Act of 1789. Part of it states and I quote;

''all cases affecting ambassadors, other public ministers and consuls,"

That is, the supreme Court Supreme Court shall have original jurisdiction in suits against ambassadors, other public ministers and consuls.