SSH into the ESXi host and run
lsusb -v | grep -e Bus -e iSerial
This will display all connected USB devices that the ESXi host can see along with the Bus and ID.
If your USB device is not showing up, it could be that the ESXi host does not have the driver for the USB controller you have the device plugged into. Try another USB port.
Once you have identified your device and the ID you can use this information to passthrough the correct USB bus to your VM.
Login to the ESXi host via vSphere or the WebUI and go to the passthrough screen. Single click on the USB bus that you want to passthrough, then look towards the bottom. You should see detailed information regarding the USB chip you just selected. This info should include the ID and Device ID, these numbers should correspond to the output you saw earlier. If the IDs do not match, keep looking through the devices until you find the ID that matches the USB devices that you want to passthrough.