What type of drive is it and how is it connected to your Mac? Does the drive eject the disk or just not display it on the Desktop? If the latter do you have the Finder preferences set to show CDs/DVDs on the Desktop? If the former try using a CD cleaning disc in the optical drive. They can be purchase at any electronics store. Only use the dry type. You may have dust, etc. on the lens.
Are these blank discs, discs with content or both?
There was a bug in the early versions of Mojave that would not display a blank CD in the optical drive. It would display burned discs but not blank discs. If you're not running the latest Mojave version update to it.
Also boot into Safe Mode, Use safe mode to isolate issues with your Mac, and try using the optical drive from there.
NOTE: Safe Mode boot can take up to 10 minutes as it's doing some cache cleaning, volume verifying and directory repairing.
