It's difficult to tell the actual size and proportions from those photos. Does it have any makers logo or part numbers?
Generally, for the commonest styles, either the back half of the shell would unscrew from the front half, or you need to hold the connector core (eg. part in a socket) and unscrew the whole shell from it.
It looks like an MS (Mil Spec) connector. Does it have lugs for a locking ring?
Search by diameter of the body, number of pins and arrangement of pins to narrow down the connector series.
The backshells of MS connectors are threaded and screw on. In your case, it might be molded on.
If you have to order one, the connector body, pins and backshell may need to be ordered separately. The pins/sockets are usually available in crimp or solder-cup style.
It looks like a cheap(er) plastic one - we don't use those because they aren't as strong as the metal ones, yet the price isn't a great deal cheaper.
We have come across occasional ones though, and (as I recall) the black part of the cable end unscrews from the main black body.
We use 3 pin, 4 pin, and 7 pin Amphenol type connectors, and fit upwards of a thousand every year. Luckily, we don't actually buy most of them - on the larger orders the customer usually provides both the connectors, and the unit they want fitting on, and we just fit them.
Agreed, you need to hold the connector core and unscrew the rear half of the shell.
The front half appears to be free to rotate for locking on a socket, so you cannot hold it by that.