I've been given this signal and asked to sketch a frequency domain representation how do i do that? how do you know which frequency components are present in the signal?
This is a classical example of beat. This means that the signal (assuming that it is periodic and extends to plus and minus infinity) contains only two frequencies with the same amplitude. The frequency of the sine wave which seems to enclose the signal will be equal to the difference between the two frequencies. The frequency of the sine wave which seems to be modulated by the enclosing wave will be the mean of the two frequencies which are present in the signal.
Fourier transform is one of possible tools to use in order to see what is the frequency content of the time domain signal and the other way around (in this case we use inverse Fourier transform). The Fourier transform decomposes a function of time (a signal) into the frequencies that make it up (c/p from Wikipedia)-> there is a lot of material, just google it.