How do you know positive pin of transistor?

To identify the positive pin of a transistor, you can refer to its datasheet, which provides pin configurations for specific transistor models. For bipolar junction transistors (BJTs), the positive pin is typically the collector for NPN transistors and the emitter for PNP transistors. Additionally, in a circuit, you can use a multimeter in diode mode to test the connections: the base will show a forward voltage drop when connected to the positive lead of the multimeter.