They're the little shiny pointy bits sticking out of the little boxy part, or possibly the little silvery ball-thingys, if there are no shiny pointy bits. Frequently, there will be three of them. Or, if you want to find out which is which, you could look up the datasheet for the transistor. Or, if you have a multimeter with a diode check function, you can try this:http://www.allaboutcircuits.com/vol_3/chpt_4/3.html
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It really helps to know the part number, most have it stamped on the package somewhere... like...2N3904, NPN transistor. NPN transistors have a Collector, a Base, and an Emitter. Google for "2n3904 datasheet" and you will be presented with a bazmillion webpages with the datasheet. I found this looks useful. The datasheet will have similar info in a similar fashion. Be aware that some sheets are for multiple products or multiple packages of the same product, so use your thinky-brain-thing to read and understand what it says.