Be careful with your spelling -- it's vIjatlh and jIjatlh with capital i and with tlh (not thl).
The difference between the two prefixes vI- and jI- is described in the section "Verbs" of the tips and notes for the very first unit -- I suggest you go back and read them: https://www.duolingo.com/skill/kl/Useful-phrases/tips-and-notes
If you haven't looked at the tips and notes so far (or perhaps you didn't even know that they exist), then you should definitely start looking at them before starting a unit.
They are available on the website https://www.duolingo.com/ (but not, for most users, in mobile apps).
When you click on a unit name, a little window opens with a key and a lightbulb icon; the lightbulb will take you to the tips and notes for that unit.