How do you interpret FFT of an FFT of a discrete signal?

I am new to DSP & Radar domain. I have one question. Say I have a discrete time signal $x[n]$ and I take an FFT of it say the output is $X[k]$. The result what i get is frequencies present in $x[n]$.

Now what will happen if I take fft on $X[k]$ ? How would the spectrum look and what would you interpret from it?

thanks in advance !