 Donkin initially began work in the same business, and worked from September 1789 to February 1791 as bailiff at Knole House and estate for the Duke of Dorset.While working for the Duke of Dorset, Donkin consulted the engineer John Smeaton, an acquaintance of his father, as to how he could become an engineer.At Smeaton's advice in 1792 he apprenticed himself to John Hall in Dartford, Kent, who had founded the Dartford Iron Works (later J & E Hall) in 1785.