There's no safety, so you'd generally carry it on an empty chamber. It's also a bit hard to see on the original image, but there's a knife as well. The knife generally had dull sides and a sharp point, making it more of a stabbing weapon instead of a slicing one. You could use the knife on it's own, but it was more likely used in conjunction with the brass knuckles.
I'm having problems getting the embedded hyperlinked image for the knife to link properly, but you can see it here: https://one.nbstatic.fr/uploaded/20230613/10597042/thumbs/450h300f_00001_REVOLVER-COUP-DE-POING-POIGNARD-dit-APACHE-BREVETE-J.-DELEAXHE-ou-DELHAXHE---PISTOLET-SORTIE-DE-BAL.jpg
