Angle of attack is usually designed by alpha (as in alpha_prot).
Is there such a conventional notation or name for other axes? I'm particularly interested in the slip angle.
Sideslip angle is commonly notated as β (see e.g. https://en.m.wikipedia.org/wiki/Slip_(aerodynamics)).
There is only one other such angle. It is indeed the sideslip one, and its standard greek letter is $\beta$ (beta)