How make on FA donk bass

"Donk Bass" sounds are generally a product of FM synthesis. There's no FM engine in the FA. That said, if you can find a wav that's got the basic tone, you might be able to get close to that once you dial in the envelopes, filters, and a bit of drive. Not a complicated sound to try an reproduce, but it originated years ago from FM synths like the Yamaha TX81z. Don't know if the FA has any PCM-S wavs that make a good starting point off the top of my head as it's not a sound I ever use, so you'll have to audition the internal wavs + any from the various EXP libraries to find something close in tone to start with.