Many enlarger lenses have click stops that can be disengaged.  Maybe
yours has click stops that you could engage by shifting the aperture
ring towards or away from the front of the lens, or by shifting a
slider on the barrel of the lens.

If you always use one aperture, you can probably get good
at stopping it down in the dark by feel. If your lens goes
from f/3.5 to f/16 and you want f/8 or f/11, it is probably
easiest to turn the dial all the way and then back up to your
standard printing aperture.

Another thing is to get a darkroom flashlight. I use a mini
maglight with a piece of #25 gel filter in front of the lens.
It is very handy for seeing into bits of the darkroom that
the main safelights don't illuminate well.

Peter.

Perhaps not. I've never seen an enlarging lens that didn't have them,
including a Fujinon EP I've used. Perhaps your lens is simply
defective?

It probably does have click-stops.  They are most likely disengaged.  I
think with Fujinon enlarger lenses, you pull down the aperture ring to
engage or disengage f-stop detents.  Can't remember exactly.

Here's how I eliminate that happening:  I used a grain magnifier, and
always do my final focus check AFTER stopping the lens down to the
printing aperture.  To view the f-stop, I hold the palm of my hand in
the light stream under the lens and reflect some of it back onto the
f-stop markings, then stop down.  You could also use a small darkroom
flashlight instead.  If you follow this procedure, your prints will
always be in focus (some lenses, even good ones, focus shift when
stopping down), and you'll never ruin another sheet of paper by
forgetting to stop down.  You will have to get a grain magnifier, but
you should have been using one all along.