The question is: Does the federal(national) gubmint have the power to do X.
What does the 10th amendment add to that question? Nothing. It says "The powers not delegated to the United States by the Constitution" belong to the states, etc.
So how does that resolve the above question? It doesn't. You are still right where you were, asking whether or not the fedgov can do X. The 10th merely says what states can do when the feds CAN'T do X, but it does nothing to resolve the question.
The question is answered, ultimately, by the SCOTUS. And once they rule, there is no appeal, and the matter is settled.
“The 10th amendment is worthless.”
Wow, really? Is the rest of the USC worthless as well?
“The question is answered, ultimately, by the SCOTUS.”
And what do they ultimately appeal to?