How to identify JFET terminals with multimeter?
A JFET is a depletion-mode device. This means that when no voltage difference is applied between the gate and the channel, current can flow. You can verify this with the multimeter, as you should see a somewhat low-impeadance path. (I say somewhat, because this is not going to measure as "short" on most multimeters. I recall using a JFET that had about 250 Ohms resistance in it's linear region with 0V gate-source.)

The gate-source and gate-drain junctions are PN junctions. In one direction, you will measure a diode drop, the other will measure open. This allows you to determine if you are dealing with an n-channel or a p-channel JFET: if a positive gate voltage leads to a diode drop, it's an n-channel device. If a negative gate voltage leads to the diode drop, it's p-channel. 

They are quite symmetric devices, as there is no bulk to connect (like in mosfets). Because of this, you can't tell source and drain apart (if there is a difference in the first place)