I have a video project in Final Cut Pro and the audio that I need (a speaker talking directly into a microphone) resides on only one channel. I had an XLR Mic hooked up to my Sony Z7U that they were talking directly into.

How do I duplicate this audio channel into the other available channel in Final Cut Pro?

TIA!

Not sure about FCP, but in many softwares you can do so by holding the ALT key, then click on the audio region and drag it to your empty channel, release the mouse button... and done.

Hope it helps.

Double click on the clip and then in the audio section in the browser you can pan it centre and adjust the gain.

Thanks Gary! That worked, and helps immensely! Your expertise and assistance is greatly appreciated!

Not an FCP user so can't answer with software specifics but I'll concur with the principle behind Gary's advice. Split the stereo track into two separate mono tracks and delete the one that wasn't used, retaining the one containing the desired audio. Using the mixer tools, pan the resulting single mono track equally to both left and rignt output channels.

Thanks Gary! That worked, and helps immensely! Your expertise and assistance is greatly appreciated!

I am by no means an expert as an ex audio guy who has only been using FCP for a year but glad I could help.
I had to figure this out myself so it goes to show how easy FCP is to learn without the help of a manual. (someday I will read it)

And yes as mentioned if its a linked stereo track you can split it in the modify section and then delete the track you dont need, un-tick the stereo pair setting.

OR if you only select one audio track link on the left of the screen in the timeline when you insert the edit it will only drop in the audio channel you have chosen.

Audio Mixer is also one place where you can manipulate tracks easily. Send the stereo track to mono subtrack and that to master stereo track. That spreads the signal to both sides.