How do we pronounce E = mc²? This is a physics equation.
The "=" sign is read as "equals" or "is equal to", depending on your culture.
(In the latter case, "is equal to" is such a common phrase all through school that it's typically read as one word: "izziqualtu".)
The "c2" could rarely be "c [raised] to the power of 2", but is almost always "c squared" (or "c square").
Thus, "ee equals em see square[d]" or "e is equal to em see square[d]".
If you listen to this audio clip of Albert Einstein speaking in 1947, you can hear him say it as "E is equal M C square" (with letters as ee, em, see).
But nowadays it's normally pronounced as Jasper Loy answered: E equals M C squared.