Question

What for of ser shall I use?

yo- soy
tu- eres
el/ella/usted/- es
nosotros- somos
vosotros- sois
ellos/ ellas/ ustedes/- son​

Answer 1

Answer is es it’s forsure es

Answer 2

It will be (es)

Since she is asking to another student how ____ the spanish teacher?

then It will be is and is on spanish will be es