Re: 61 - 5.5 "Fisherman" prop removal
There should be a cotter pin through the hole in the flats near the nose of that thing. Look closely. Now, it may have broken off somehow, but you'll still have to clear that hole all the way through before you can remove the cap.
The cotter pin is all that holds it on. It's a slip fit over the end of the prop shaft.
Once it's off, you'll see the drive pin through the prop sleeve and the prop shaft.
That's all there is to that prop and its attachment. So, look closely, and act carefully. The cap or "nut" is available, but may not be in stock at your local Evinrude dealer, so you don't want to ruin it. Get a spare. Seriously...plus a couple of spare drive pins.
Take another look.