Are palpable supraclavicular lymph nodes usually cancer?

It depends.: Sometimes these, and other nodes are palpable because of infection. Sometimes cancer can do it. Rock hard nodes would more likely mean cancer, while soft, painful ones would point to infection.

Not necessarily: Supra-clavicular lymph nodes may be enlarged due to local or systemic infections. Unilateral enlargement of supra-clavicular lymph nodes would be more suspicious and warrant exclusion of malignancy.