A better question is "How do I NOT breed jewels?" Get a male and female together and they WILL breed. I got 5 so I could breed them for feeders. A pair formed and I got rid of the others. They breed about once a month...
The problem is that some of the babies I used to feed managed to hide in the plants and thrive in my main tank, and now they are breeding in there. I should care, but I don't, it's funny to watch 2" jewels chase off a 12" endli.
My point is they will breed if you have a male and a female, and then you have to figure out what to do with the babies... 'cause there will be lots.