Names do not have direct translations into Dovahzul. You could find the meaning behind the name and translate that, if you'd like.

"Jack" is a medeival diminutive of "John," which is the English form of "Iohannes," which is from a Hebrew word meaning "God is Gracious."

So, we can say that "Jack" could indirectly be translated to "God's Grace," or something along those lines.

Relevant Dovahzul words for that would be:

Rah - God

Dun - Grace

Most Dovah names are composed of three rotmulaag, or Words of Power. If you use those as two of your three monosyllabic Words of Power, you can find a third word that you think would fit you. Look through the Dictionary here on the site and find something that you'd like!

Dragon names don't have conjunctions, like "and," or prepositions, like "of," in them. Maybe find something that fits your personality. Mul, "strong," is one possibility, or Yol, "fire." There are plenty of options available to you. If you'd like, you can find a unique combination of three rotmulaag to create your own Dragon name from scratch! It's fairly simple and plenty of fun! Good luck!

(Sorry I didn't reply sooner. I haven't been as active on here lately.)