In this case, you want to write to ask the date of a school event. If you also explain why you would like to know this, the schoolteacher will understand your situation and positive attitude as a parent.
Conversational flow and useful expressions
A parents' meeting is usually called a hogosha-kai, hogosha-kondankai or fubo-kai. These meetings are held at the beginning of the school year and prior to a large event in order to get together and exchange information.