I am trying to find out if the pulse in the figure satisfies the Nyquist criterion for a modulation interval T. I'm used to the Nyqusit frequency, but I cannot grasp what the Nyquist criterion is about.
The Nyquist criterion for avoiding intersymbol interference (ISI) requires the pulse to have zeros at multiples of the symbol interval $T$, such that symbols do not interfere with each other. The time domain requirement is
In the frequency domain, criterion $(1)$ can be formulated as
where $H(f)$ is the Fourier transform of $h(t)$. I.e., the shifted spectra (shifted by the symbol rate) must add up to a constant.
I leave it up to you to decide whether or not the given pulse satisfies $(1)$ and $(2)$.
I suggest you go through your lectures notes because it would be surprising if the Nyquist criterion has never been mentioned and you get an exercise like this.