Amplitude and phase spectrum
The amplitude of the spectrum of this signal is related, as all pulsed signal, with the \$sinc(t)\$ function. You must find a trigonometric relationship between the coefficient associated with the sine function

$$
\dfrac{2E}{T\,j\,n\omega}
$$

and the argument of the function.

$$
n\,\omega\dfrac{\tau}{2}
$$

Check out the link, and see that there is a relationship between the pulse width and frequency of the \$sinc(t)\$ function.