Hello Techzenit,
That question is very very broad.
Are you trying to determine what the vCenter portgroup is allowing/trunked through to NSX-T?
or
Are you wanting to know what segments are being bridge to what VLANs?
or
Are you looking to generate a report using an API to determine what is in use and what is not in use?
The vCenter portgroup being used for bridging can allow ALL VLANs through 0-4096, or selective VLANs through, or a single VLAN through. It just depends on how the portgroup is configured.
What is being allowed through is different that what is actually being used. You can allow all VLANs through, but only have a couple of NSX-T Segments bridging over to 3 or 4 VLANs.
If that does not answer your question then more elaboration is needed on your main question
