Clean the trans off with some brake cleaner or something, make sure the fluid level is correct and let the car run, but don't drive it anywhere. Then take a look and see if you can tell where it is coming from. ATF is thin enough that in the course of driving, it will blow all over the place and make it hard to find the source of the leak. Common sources are the pan gasket, dipstick tube seal, shift shaft seal (real common) and the front pump seal (which usually means the front pump bushing is worn out too)