OK no worries, you've come to the right place. Since it is already soldered in, it becomes a bit "trickier" - refer following pic

You put the meter in diode test mode - Pos (Red) on A1 (Anode) with Neg (Black) on K (Kathode). You should see app 0.4V. Switch Pos to A2 and it should be the same !
If you reverse the leads, it should be open cct = same readings as with leads free.
In circuit, there is no way to predict what you'll see, as the "test voltage" may trigger other components or charge up caps or connect to chokes etc etc. Only experience may help here, BUT it should be a similar pattern ie 1 set higher / the other lower, and definitely not 0V. See how you go