It's best to put a large gathering area {i} {g} out there encompassing land with various examples of the fruits, vegetables, leafy greens, trees, berries etc. When the time comes for those to be "harvestable", the dorfs will just... know. And they'll deal with it. I tend to put a small storage stockpile for "furniture - large tools" in the middle of the gathering plot, so that they can leave the stepladders there. The occasional stepladder gets stolen by a monkey, but in general, it's a pretty good system. If the situation is rife, I surround the stockpile with cage/stonefall traps, and have lots of monkeys trapped to death or caged. And my dorfs don't have to travel far to get a stepladder for fruit picking.
In all fairness, eggplant is pretty gross so you wouldnt want to pick them anyways..
Personal preference isn't really the point here. I love eggplant (especially roasted with a little olive oil and salt) and you don't. There are dorfs out there with similar preference differences. One might love blackberries, another might not care for them, a third might only like them brewed.
I've had someone tell me that they don't allow the dorfs to cook any of the delicious offal that they generate from slaughtering animals, not even lambs kidneys or lights, or chicken livers, which we real life humans eat regularly. Seems odd that some people in the real world don't eat offal: they promote good health and are also very tasty (don't believe me? You probably shouldn't eat anything made of mince then. Ever. Yes, that includes hamburger mince, sausages, and pies & pasties).... Thus the comment in my signature about mule spleens. These same players who don't allow mule spleen roasts have their dorfs occasionally desperate for food or booze... Because they aren't utilising every part of the beast, as nature (and dorfs) intended. If you allow them to gather eggplants, then there might be more berries uneaten for you to make booze with. More booze with more variety = better morale = better game. Consider that.