You don't, unless it's to create off topic arguments/trolling. To answer your question if you know the sex, you say the sex. If not you use sexless pronouns l

You don't, unless it's to create off topic arguments/trolling. To answer your question if you know the sex, you say the sex. If not you use sexless pronouns like "their" and "they" even if they are not 'proper' by old strict standards, basically they are, because language evolves.