Cách sử dụng
The expression "speak of" is used to refer to something that has just been mentioned or discussed. For example, if someone says "Let's talk about the weather," and then you say "Oh, it's really hot today," you could then say "Speaking of hot weather, did you know there's a heatwave coming?" So it's a way to transition from one topic to another that is related to the first one in some way.