How do I know what version of Thunderbolt firmware I have running?

Yes, I do have a Thunderbolt Display connected and, yes, the Display itself has firmware (and, as you can see, the ATD cable does have its own serial number - if it's replaced, of course, the serial number changes).

Clinton

If you do software update and no TB firmware is listed then you have the most recent version for your model Mac computer.

Doesn't really matter what version you have. If it doesn't show up on sofware update then you don't need any newer version.

To see what version you have go to the Apple Logo icon in the menu bar and sel;ect "About This Mac" Then click the More Info button then the System Report button. Hardware section, Thunderbolt.

You can get the actual version of your Display firmware by accessing the Thunderbolt hardware section as LL describes:

I'm fairly certain that 22.2 if the latest firmware version for the Display.

Clinton

Actually that firmware version number is for the TB hardware in the Mac. Not for a TB display connected to it. In fact I don't see any listing for the display in your SS. If you have a TB display connected. Only the cable FW and serial number. God knows why a cable would have a serial number and FW version.