Hi Helenwell,
Switch your function generator to sinewave and adjust it to the line
frequency. Set the output voltage at 1 volt. Connect it to your
transformer, any way you like and measure the opposite side of
your transformer. If the output signal is about nine times larger than
the input signal, you're measuring at the primary side of your transformer.
If the output signal is about nine times smaller than the input signal,
you're measuring at the secundary of your transformer. You don't
have to be afraid to perform this measurement, you won't damage your
transformer or your scope, it's absolutely safe.
Regards,
on1aag.