Godfrey Kneller was the leading portrait artist in Britain during the late 17th and early 18th centuries. In 1711, the year this was painted, Sir Christopher Wren had finally finished St Paul's Cathedral, which is alluded to within the painting by the pair of dividers he holds, the copy of Euclid and the plan of the west end of the new St Paul's.
This is a copy, the original can be found in the National Portrait Gallery.