There's two ways you can do it.
If you just want to get a "quick and dirty" reading, you can turn your volume and tone controls all the way up and plug a cable into your output jack. Then touch one of the probes of your ohm meter (or multi-meter) to the shaft of the cable connector and the other end to the tip. Polarity shouldn't matter. You should get a reading (depending on the pickup) somewhere in between 6 and 15 ohms. On a Seth Lover, I'd expect to see something between 6 and 8 ohms.
If you want a more accurate reading, you can also unsolder the + and - pickup wires from the pots (or switch, depending where they're connected). If it's a single braided wire, then the outside braided portion will be the ground, and the inner core will be the positive. As above, touch one of the ohm/multi-meter probes to the pos and the other to the ground. Again, you should get a reading somewhere in between 6 and 15 ohms (depending on the number of winds in the pickup).
If you get no reading, it's possible that something has gone wrong inside the pickup. If that's the case, you'll probably want to take it to a repair shop and see if they can fix it. It probably won't cost too much to fix. Even a complete rewind (if the pickup is totally dead) should be about $50 or less.
This is, of course, assuming that you're not getting any sound out of the guitar.
If you ARE getting sound out of the guitar when it's plugged in, and you're not getting a reading with your ohm meter, then it's possible that your ohm meter is not working properly.
Hope that helps some.