Here are a few ways to answer:
If you know the teacher's name:
* "El profesor de español es [Name]." (The Spanish teacher is [Name].)
If you don't know the teacher's name:
* "No lo sé." (I don't know.)
* "No estoy seguro/a." (I'm not sure.)
* "¿Quién es?" (Who is it?) - This is a question back to the person asking.
If you know the teacher but don't remember their name:
* "Es la persona que está ahí." (It's the person who is over there.)
* "Es el/la profesor/a que tiene el libro de español." (It's the teacher who has the Spanish book.)
In a formal setting, you might say:
* "Permítame consultar." (Let me check.)
Remember to use the correct gender for "profesor" or "profesora" based on the teacher's gender.