How to find a compatible DVD player for macOS Mohave?

Depends on what you mean by "DVD player".

If you mean a set top DVD player like the ones you connect to a TV, then none of those will work.

If you mean an DVD disc drive to read CDs and DVDs on a computer, then pretty much any external USB DVD drive should work with Mojave.

I use a Gotega branded one with my Mac:

But you can sue anything else, like Dell, HP or even Apple's own super drive though they don't make it anymore.

click here ➜ Gotega External USB Drive - Amazon.com

click here ➜ Dell USB DVD Drive - Amazon.com

click here ➜ HP Portable Slim DVD drive - Amazon.com

and if you mean software to play dvds on the computer then try vlc player it's free