male and female PKs are not too hard to distinguish. a male pk and a female VT however can be very easily confused, particularly if the female VT is very young.the fins are really the best way to tell the pk sexes apart. the males anal fin is much longer at the back and will have a very fine, sharp and often quite long, point to it. his tail will be slightly longer and have a wider spread on it, although you may only notice this when flaring. his colors are generally more intense. his body will be altogether more muscular looking than that of a female.
NEVER make a finale judgment by the presence of an "egg spot"..NEVER! its a load of BULL that this mean 100% its female. young males, especialy young pks for some reason will often show a "false ovipositor" which is just an extension of their anus. i think the reason for this is, as alot of young pk males are being sold as female, its not uncommon to see several in one tank, and the lower ranking males show an egg spot and stress bars to show submissiveness and also to disguise them selves as a female to avoid conflict with with the dominant males.
telling a young vt female from a young pk male can prove trickier, especially if she flares a lot. but again her colors will be less intense, when she flare she wont have the big beard of a pk male, in good condition she will be fat and eggy. her anal fin will be very similar to a PKs but a little longer and will usually lack the defined point on a pk. her tail will be rounder and the outer rays on her tail will curve into each other, whereas on a PK they are straight.
hers a few pics, first is a pk male, then a pk female and then a flaring pic of a vt female for comparison
hope this helps