D&D is written for humans. It's written by humans from the perspective of humans, and when comparisons are made, they're made to a baseline human. Things that aren't outright stated in the D&D should be assumed to be human-normal. Huge parts of the game are built around the human as the standard, from armor class (the default AC of 10 is the AC of your average unarmored human) to attack rolls (your average unarmed human with no special training has about a 50% chance -- 10+ on a d20 -- of hitting another average unarmored human with a punch) to saving throws (default DCs are set according to what your average human could resist, dodge, or survive) to skill checks (DC 10 is something your average unskilled guy could succeed at about 50% of the time). With this humanocentric view, it should be clear that if there is no listed answer to a question, the answer almost certainly is the same as asking the question about a human.
How do bugbears poop? Just like a human.
Where do gnomes have body hair? In the same places humans do.
How good is an aboleth's sense of smell? About as good as a human.
How spicy is too spicy to an aasimar? About as much as a human would consider too spicy.