The Secretariat of the Commonwealth of Nations is located in

The Commonwealth of Nations (formerly the British Commonwealth) is a voluntary association of 56 independent countries, most of which are former territories of the British Empire. Its Secretariat, the principal administrative body of the organisation, is located in London, United Kingdom.

The Commonwealth Secretariat has been based at Marlborough House in London since 1965, when it was established. It is headed by the Commonwealth Secretary-General and coordinates activities across member states, including promoting democracy, human rights, and economic development.

The other options are incorrect:

• New York is the headquarters of the United Nations.
• Paris is the headquarters of UNESCO and was historically associated with French-speaking international organisations.
• Canada is a Commonwealth member state, not the location of its Secretariat.

London was chosen as the Secretariat's location partly because of the United Kingdom's historical role at the centre of the British Empire, from which the Commonwealth evolved.