They are right at the back of the clock, 2 small studs with nuts on them, the blue (delicate) pcb is under the nuts.
If you are not sure about how to use a multimeter, you need to be careful. There will be plenty of "how to" vids on YouTube, or get a mate to run through it with you.
Basically, set it to read DC Volts, then set the scale to the 20 Votts Range (or the nearest to that). Then make sure the black lead is in the hole marked "common" or "negative" (usually coloured black, like the lead). Then put the red lead into the hole on the meter marked "+ve" or "V" (note = do NOT plug it into any socket marked "A", "mAh", "20A" or similar).
Note = you cannot get a shock, so it is ok to do the following with your fingers (or those of an assistant as you may need 3 hands

)
Now attach the black lead to a bright bit of metal work on the body / dash etc of the van (this is called "earthing" it).
Now touch the red lead
carefully onto one of the 2 terminals on the back of the clock (it does not matter which) and look at the meter (assistant comes in handy here). It will either read about 12.5 volts, or next to nothing. Make a mental note.
Now touch the red leads probe onto the other terminal on the back of the clock and note the reading.
Now, one of them should be showing 12.5 (ish) volts and the other should be reading very close to zero volts.
If neither of them read 12 volts, then the 12 volt feed to the clock is duff (and you need to trace back along the pcb to find out why).
If both of them read 12 volts, then the earth to the clock is duff (and you need to trace back along the pcb to find out why).
If one of them reads 12 volts and the other reads zero or nearly zero then the clock might be faulty (less likely in view of your recent circumstances).
It has to be said that without some basic knowledge of how 12 volt DC circuits work, much of what I have described will not help you find the reason why you are not getting the readings you should
Mine was just a simple bad connection under the "earthing" nut on the clock, where it is
supposed to make contact with the coppery bit on the blue PCB. A simple clean up and it started working again.
As so often, frustrating for me (us) as, if it was in front of me, I could find the problem in 5 minutes or less.
Good luck with it.