What kind of a connector is needed to connect a Nikon COOLPIX P310 camera to an iMac computer

If you use the cable that came with the camera, then you can use any of the adapters that I posted above.

If that is not working, then you can remove the card from the camera and use an external card reader.

You need a USB-C to USB-A adapter.

You can use Apple's adapter.

USB-C to USB Adapter - Apple

Or third party USB-C to USB-A adapters.

https://www.amazon.com/dp/B0B9N3QSL3/ref=sspa_dk_detail_0?

https://www.target.com/p/philips-usb-c-to-3-0-usb-a-female-adapter/-/A-79804275