The position of the marker is an estimate, based on descriptions below that it was 'opposite the Nullah' and 'below the Headquarters House'. (View the marker on the 1901 Map to see its position relative to the nullah and Headquarters House.)
In Carl Smith's article, The German Speaking Community in Hong Kong 1846-1918, he writes that the club 'was started in 1859 in Wanchai in an unpretentious building. It was below the Headwuarters House ...'. He continues, 'The club moved in 1865 to a new building erected by Gustav Overbeck at the top of Wyndham Street just south of D'Aguilar Street.' (There's a separate page on Gwulo for that second location of the German Club.)
The German Club must have moved out in early 1865, as by 1st June 1865 George Mitchellmore was advertising the building had become The Eastern Private Family Hotel: