How to pronounce G°? To denote standard state like enthalpy of formation in standard state, or change in Gibbs free energy in standard state, we use a degree-like symbol above the $G$ as in $\Delta G^0$. How should I refer to this superscript in spoken language?
G-zero and G-prime.

G-zero has also in my presence been referred to as "G-ought", "G-nought", "standard-G" or "G at standard state". I am particular towards "G-zero" myself. (Mostly because of a witty limerick I heard during my studies. Zero rhymes with hero.)