How to measure VSWR of a single connector?
Put the connector on a long piece of coax instead of a short one. I'd use 1 m or more, given your 9 GHz bandwidth.

Then use time domain gating (a feature available on many VNAs) to measure only the reflections coming from the connector and not the reflections from the open far end of the coax. Time domain gating means the VNA will transform the response to time domain, apply a window around a part of the time-domain response you specify, then transform the result back to frequency domain before displaying the results.

This would be a one-port measurement. The second port of the VNA would not be used.