In Star Wars, has it been mentioned how the clone troopers & any other clones are created? By that I mean, was somatic cell nuclear transfer the method that was used?
There's no description of the process by which clones are initiated in the films or any of the canon books, other than that donor DNA (courtesy of Jango Fett for the clone troopers) is required.
Interestingly, fresh infusions of DNA are evidently required on an ongoing basis in order to prevent the clones from becoming sluggish and incompetent.
Lama Su: Ever since the unfortunate Death of Jango Fett, we have had to stretch his DNA to produce more clones. However, I have noticed this unit of clones have been ... deficient
Moving into the Legends canon, we have this description in the Dark Force Sourcebook
Cloning takes a Human cell, and duplicates its genetic code. The code is implanted in a cell and as the cell grows into a Human, it will create an exact duplicate of the cell donor