When written by using Alphabet, this expression is as follows (in its closest approximation):
Kondo itsu aemasu ka?
For further explanation (I don't know whether you need it or not) --
Kondo = Next time
Itsu = when
Aemasu = can meet
Ka = question conjugation (placed at the end of regular sentence, makes question form)
For the third word, you would pronounce it as though you are in vocal practice for pronounciation -- A E I O U.
There might be some other expressions depending on courteous or formal, but this would be the standard.

Yours,