Yes!! neutered dogs can have sex if they want, getting them to show that interest is the challenging part.
1- You have to be aware, mounting, and mating for dogs, even tho is highly sexual, it is also a dominance and controlling behaviour.
2- Dogs are turned on by bitches, not humans. If he already mount you, then he already sees you as his bitch, but if he hasn't you have to make him understand that you're his bitch.
How can you become his bitch? First you have to offer him your pussy, he has to know it, he has to smell it, encourage him to lick it, do it everyday even if you're not in the mood, obviously when you're horny, offer him your pussy, let him eat you out. Make sure you do that until you start ovulating (All of this while you're on your fours), and encourage him to dominate you, get him on your back, touch his dick, suck his balls, his cock, stick your pussy the closer you can to his dick, this way, you're letting him understand, that you're his bitch, and that he can take you whenever he wants. The best time to try being inseminated by him is when you're ovulating, even neutered dog get aroused by a bitch in heat, and they can smell and differentiate you being fertile, that might arouse him, he might try to breed you, let him do it, give him a little help, but let him know that yes, you're his bitch and that you want to be inseminated by him, if you do that for like two months, you might be able to get him to knot you someday. However is all about patience, and if after all of that he still doesn't show interest, then he probably was neutered very young and didn't reach that sexual maturity level.