It makes sense to reduce Traveling Salesman problem to these problems, not the other way around.

This problem is more general than Clique.

Reduce Clique to it: given a graph G, add k isolated points. Then there is an independent set of size k, and the question is only about a clique.

This I don't know immediately, but it is a well-known problem, so try searching the web. If you still can't find the solution, let us know again.